2008-10-23 05:26:29 +00:00
|
|
|
#ifndef _ASM_X86_ASM_H
|
|
|
|
|
#define _ASM_X86_ASM_H
|
2008-01-30 12:30:06 +00:00
|
|
|
|
2008-06-16 23:08:17 +00:00
|
|
|
#ifdef __ASSEMBLY__
|
|
|
|
|
# define __ASM_FORM(x) x
|
2013-08-29 19:13:04 +00:00
|
|
|
# define __ASM_FORM_RAW(x) x
|
2011-07-19 12:00:45 +00:00
|
|
|
# define __ASM_FORM_COMMA(x) x,
|
2008-06-16 23:08:17 +00:00
|
|
|
#else
|
|
|
|
|
# define __ASM_FORM(x) " " #x " "
|
2013-08-29 19:13:04 +00:00
|
|
|
# define __ASM_FORM_RAW(x) #x
|
2011-07-19 12:00:45 +00:00
|
|
|
# define __ASM_FORM_COMMA(x) " " #x ","
|
2008-06-16 23:08:17 +00:00
|
|
|
#endif
|
2008-01-30 12:31:26 +00:00
|
|
|
|
x86/asm: Fix inline asm call constraints for GCC 4.4
The kernel test bot (run by Xiaolong Ye) reported that the following commit:
f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang")
is causing double faults in a kernel compiled with GCC 4.4.
Linus subsequently diagnosed the crash pattern and the buggy commit and found that
the issue is with this code:
register unsigned int __asm_call_sp asm("esp");
#define ASM_CALL_CONSTRAINT "+r" (__asm_call_sp)
Even on a 64-bit kernel, it's using ESP instead of RSP. That causes GCC
to produce the following bogus code:
ffffffff8147461d: 89 e0 mov %esp,%eax
ffffffff8147461f: 4c 89 f7 mov %r14,%rdi
ffffffff81474622: 4c 89 fe mov %r15,%rsi
ffffffff81474625: ba 20 00 00 00 mov $0x20,%edx
ffffffff8147462a: 89 c4 mov %eax,%esp
ffffffff8147462c: e8 bf 52 05 00 callq ffffffff814c98f0 <copy_user_generic_unrolled>
Despite the absurdity of it backing up and restoring the stack pointer
for no reason, the bug is actually the fact that it's only backing up
and restoring the lower 32 bits of the stack pointer. The upper 32 bits
are getting cleared out, corrupting the stack pointer.
So change the '__asm_call_sp' register variable to be associated with
the actual full-size stack pointer.
This also requires changing the __ASM_SEL() macro to be based on the
actual compiled arch size, rather than the CONFIG value, because
CONFIG_X86_64 compiles some files with '-m32' (e.g., realmode and vdso).
Otherwise Clang fails to build the kernel because it complains about the
use of a 64-bit register (RSP) in a 32-bit file.
Reported-and-Bisected-and-Tested-by: kernel test robot <xiaolong.ye@intel.com>
Diagnosed-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: LKP <lkp@01.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang")
Link: http://lkml.kernel.org/r/20170928215826.6sdpmwtkiydiytim@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-28 21:58:26 +00:00
|
|
|
#ifndef __x86_64__
|
|
|
|
|
/* 32 bit */
|
2008-06-16 23:08:17 +00:00
|
|
|
# define __ASM_SEL(a,b) __ASM_FORM(a)
|
2013-08-29 19:13:04 +00:00
|
|
|
# define __ASM_SEL_RAW(a,b) __ASM_FORM_RAW(a)
|
2008-01-30 12:30:06 +00:00
|
|
|
#else
|
x86/asm: Fix inline asm call constraints for GCC 4.4
The kernel test bot (run by Xiaolong Ye) reported that the following commit:
f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang")
is causing double faults in a kernel compiled with GCC 4.4.
Linus subsequently diagnosed the crash pattern and the buggy commit and found that
the issue is with this code:
register unsigned int __asm_call_sp asm("esp");
#define ASM_CALL_CONSTRAINT "+r" (__asm_call_sp)
Even on a 64-bit kernel, it's using ESP instead of RSP. That causes GCC
to produce the following bogus code:
ffffffff8147461d: 89 e0 mov %esp,%eax
ffffffff8147461f: 4c 89 f7 mov %r14,%rdi
ffffffff81474622: 4c 89 fe mov %r15,%rsi
ffffffff81474625: ba 20 00 00 00 mov $0x20,%edx
ffffffff8147462a: 89 c4 mov %eax,%esp
ffffffff8147462c: e8 bf 52 05 00 callq ffffffff814c98f0 <copy_user_generic_unrolled>
Despite the absurdity of it backing up and restoring the stack pointer
for no reason, the bug is actually the fact that it's only backing up
and restoring the lower 32 bits of the stack pointer. The upper 32 bits
are getting cleared out, corrupting the stack pointer.
So change the '__asm_call_sp' register variable to be associated with
the actual full-size stack pointer.
This also requires changing the __ASM_SEL() macro to be based on the
actual compiled arch size, rather than the CONFIG value, because
CONFIG_X86_64 compiles some files with '-m32' (e.g., realmode and vdso).
Otherwise Clang fails to build the kernel because it complains about the
use of a 64-bit register (RSP) in a 32-bit file.
Reported-and-Bisected-and-Tested-by: kernel test robot <xiaolong.ye@intel.com>
Diagnosed-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: LKP <lkp@01.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: f5caf621ee35 ("x86/asm: Fix inline asm call constraints for Clang")
Link: http://lkml.kernel.org/r/20170928215826.6sdpmwtkiydiytim@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-28 21:58:26 +00:00
|
|
|
/* 64 bit */
|
2008-06-16 23:08:17 +00:00
|
|
|
# define __ASM_SEL(a,b) __ASM_FORM(b)
|
2013-08-29 19:13:04 +00:00
|
|
|
# define __ASM_SEL_RAW(a,b) __ASM_FORM_RAW(b)
|
2008-06-16 23:08:17 +00:00
|
|
|
#endif
|
2008-01-30 12:30:06 +00:00
|
|
|
|
2011-07-19 11:59:51 +00:00
|
|
|
#define __ASM_SIZE(inst, ...) __ASM_SEL(inst##l##__VA_ARGS__, \
|
|
|
|
|
inst##q##__VA_ARGS__)
|
2013-08-29 19:13:04 +00:00
|
|
|
#define __ASM_REG(reg) __ASM_SEL_RAW(e##reg, r##reg)
|
2008-01-30 12:30:06 +00:00
|
|
|
|
2008-06-16 23:08:17 +00:00
|
|
|
#define _ASM_PTR __ASM_SEL(.long, .quad)
|
|
|
|
|
#define _ASM_ALIGN __ASM_SEL(.balign 4, .balign 8)
|
2008-01-30 12:31:26 +00:00
|
|
|
|
2008-08-19 01:13:33 +00:00
|
|
|
#define _ASM_MOV __ASM_SIZE(mov)
|
2008-06-16 23:08:17 +00:00
|
|
|
#define _ASM_INC __ASM_SIZE(inc)
|
|
|
|
|
#define _ASM_DEC __ASM_SIZE(dec)
|
|
|
|
|
#define _ASM_ADD __ASM_SIZE(add)
|
|
|
|
|
#define _ASM_SUB __ASM_SIZE(sub)
|
|
|
|
|
#define _ASM_XADD __ASM_SIZE(xadd)
|
2017-05-01 22:47:41 +00:00
|
|
|
#define _ASM_MUL __ASM_SIZE(mul)
|
2008-08-19 01:13:33 +00:00
|
|
|
|
2008-06-24 14:37:57 +00:00
|
|
|
#define _ASM_AX __ASM_REG(ax)
|
2008-06-24 20:36:31 +00:00
|
|
|
#define _ASM_BX __ASM_REG(bx)
|
|
|
|
|
#define _ASM_CX __ASM_REG(cx)
|
2008-06-24 14:37:57 +00:00
|
|
|
#define _ASM_DX __ASM_REG(dx)
|
2008-08-19 01:13:33 +00:00
|
|
|
#define _ASM_SP __ASM_REG(sp)
|
|
|
|
|
#define _ASM_BP __ASM_REG(bp)
|
|
|
|
|
#define _ASM_SI __ASM_REG(si)
|
|
|
|
|
#define _ASM_DI __ASM_REG(di)
|
2008-01-30 12:30:06 +00:00
|
|
|
|
2016-06-08 19:38:40 +00:00
|
|
|
/*
|
|
|
|
|
* Macros to generate condition code outputs from inline assembly,
|
|
|
|
|
* The output operand must be type "bool".
|
|
|
|
|
*/
|
|
|
|
|
#ifdef __GCC_ASM_FLAG_OUTPUTS__
|
|
|
|
|
# define CC_SET(c) "\n\t/* output condition code " #c "*/\n"
|
|
|
|
|
# define CC_OUT(c) "=@cc" #c
|
|
|
|
|
#else
|
|
|
|
|
# define CC_SET(c) "\n\tset" #c " %[_cc_" #c "]\n"
|
|
|
|
|
# define CC_OUT(c) [_cc_ ## c] "=qm"
|
|
|
|
|
#endif
|
|
|
|
|
|
2008-02-04 15:47:56 +00:00
|
|
|
/* Exception table entry */
|
2009-08-31 18:57:20 +00:00
|
|
|
#ifdef __ASSEMBLY__
|
2016-02-17 18:20:12 +00:00
|
|
|
# define _ASM_EXTABLE_HANDLE(from, to, handler) \
|
2012-04-20 23:57:35 +00:00
|
|
|
.pushsection "__ex_table","a" ; \
|
2016-02-17 18:20:12 +00:00
|
|
|
.balign 4 ; \
|
2012-04-21 00:12:48 +00:00
|
|
|
.long (from) - . ; \
|
|
|
|
|
.long (to) - . ; \
|
2016-02-17 18:20:12 +00:00
|
|
|
.long (handler) - . ; \
|
2012-04-20 23:57:35 +00:00
|
|
|
.popsection
|
|
|
|
|
|
2016-02-17 18:20:12 +00:00
|
|
|
# define _ASM_EXTABLE(from, to) \
|
|
|
|
|
_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
|
|
|
|
|
|
|
|
|
|
# define _ASM_EXTABLE_FAULT(from, to) \
|
|
|
|
|
_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
|
|
|
|
|
|
|
|
|
|
# define _ASM_EXTABLE_EX(from, to) \
|
|
|
|
|
_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
|
2014-04-17 08:17:05 +00:00
|
|
|
|
locking/refcounts, x86/asm: Implement fast refcount overflow protection
This implements refcount_t overflow protection on x86 without a noticeable
performance impact, though without the fuller checking of REFCOUNT_FULL.
This is done by duplicating the existing atomic_t refcount implementation
but with normally a single instruction added to detect if the refcount
has gone negative (e.g. wrapped past INT_MAX or below zero). When detected,
the handler saturates the refcount_t to INT_MIN / 2. With this overflow
protection, the erroneous reference release that would follow a wrap back
to zero is blocked from happening, avoiding the class of refcount-overflow
use-after-free vulnerabilities entirely.
Only the overflow case of refcounting can be perfectly protected, since
it can be detected and stopped before the reference is freed and left to
be abused by an attacker. There isn't a way to block early decrements,
and while REFCOUNT_FULL stops increment-from-zero cases (which would
be the state _after_ an early decrement and stops potential double-free
conditions), this fast implementation does not, since it would require
the more expensive cmpxchg loops. Since the overflow case is much more
common (e.g. missing a "put" during an error path), this protection
provides real-world protection. For example, the two public refcount
overflow use-after-free exploits published in 2016 would have been
rendered unexploitable:
http://perception-point.io/2016/01/14/analysis-and-exploitation-of-a-linux-kernel-vulnerability-cve-2016-0728/
http://cyseclabs.com/page?n=02012016
This implementation does, however, notice an unchecked decrement to zero
(i.e. caller used refcount_dec() instead of refcount_dec_and_test() and it
resulted in a zero). Decrements under zero are noticed (since they will
have resulted in a negative value), though this only indicates that a
use-after-free may have already happened. Such notifications are likely
avoidable by an attacker that has already exploited a use-after-free
vulnerability, but it's better to have them reported than allow such
conditions to remain universally silent.
On first overflow detection, the refcount value is reset to INT_MIN / 2
(which serves as a saturation value) and a report and stack trace are
produced. When operations detect only negative value results (such as
changing an already saturated value), saturation still happens but no
notification is performed (since the value was already saturated).
On the matter of races, since the entire range beyond INT_MAX but before
0 is negative, every operation at INT_MIN / 2 will trap, leaving no
overflow-only race condition.
As for performance, this implementation adds a single "js" instruction
to the regular execution flow of a copy of the standard atomic_t refcount
operations. (The non-"and_test" refcount_dec() function, which is uncommon
in regular refcount design patterns, has an additional "jz" instruction
to detect reaching exactly zero.) Since this is a forward jump, it is by
default the non-predicted path, which will be reinforced by dynamic branch
prediction. The result is this protection having virtually no measurable
change in performance over standard atomic_t operations. The error path,
located in .text.unlikely, saves the refcount location and then uses UD0
to fire a refcount exception handler, which resets the refcount, handles
reporting, and returns to regular execution. This keeps the changes to
.text size minimal, avoiding return jumps and open-coded calls to the
error reporting routine.
Example assembly comparison:
refcount_inc() before:
.text:
ffffffff81546149: f0 ff 45 f4 lock incl -0xc(%rbp)
refcount_inc() after:
.text:
ffffffff81546149: f0 ff 45 f4 lock incl -0xc(%rbp)
ffffffff8154614d: 0f 88 80 d5 17 00 js ffffffff816c36d3
...
.text.unlikely:
ffffffff816c36d3: 48 8d 4d f4 lea -0xc(%rbp),%rcx
ffffffff816c36d7: 0f ff (bad)
These are the cycle counts comparing a loop of refcount_inc() from 1
to INT_MAX and back down to 0 (via refcount_dec_and_test()), between
unprotected refcount_t (atomic_t), fully protected REFCOUNT_FULL
(refcount_t-full), and this overflow-protected refcount (refcount_t-fast):
2147483646 refcount_inc()s and 2147483647 refcount_dec_and_test()s:
cycles protections
atomic_t 82249267387 none
refcount_t-fast 82211446892 overflow, untested dec-to-zero
refcount_t-full 144814735193 overflow, untested dec-to-zero, inc-from-zero
This code is a modified version of the x86 PAX_REFCOUNT atomic_t
overflow defense from the last public patch of PaX/grsecurity, based
on my understanding of the code. Changes or omissions from the original
code are mine and don't reflect the original grsecurity/PaX code. Thanks
to PaX Team for various suggestions for improvement for repurposing this
code to be a refcount-only protection.
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Hans Liljestrand <ishkamiel@gmail.com>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: Jann Horn <jannh@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arozansk@redhat.com
Cc: axboe@kernel.dk
Cc: kernel-hardening@lists.openwall.com
Cc: linux-arch <linux-arch@vger.kernel.org>
Link: http://lkml.kernel.org/r/20170815161924.GA133115@beast
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-08-15 16:19:24 +00:00
|
|
|
# define _ASM_EXTABLE_REFCOUNT(from, to) \
|
|
|
|
|
_ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
|
|
|
|
|
|
2014-04-17 08:17:05 +00:00
|
|
|
# define _ASM_NOKPROBE(entry) \
|
|
|
|
|
.pushsection "_kprobe_blacklist","aw" ; \
|
|
|
|
|
_ASM_ALIGN ; \
|
|
|
|
|
_ASM_PTR (entry); \
|
|
|
|
|
.popsection
|
2015-05-13 17:42:23 +00:00
|
|
|
|
|
|
|
|
.macro ALIGN_DESTINATION
|
|
|
|
|
/* check for bad alignment of destination */
|
|
|
|
|
movl %edi,%ecx
|
|
|
|
|
andl $7,%ecx
|
|
|
|
|
jz 102f /* already aligned */
|
|
|
|
|
subl $8,%ecx
|
|
|
|
|
negl %ecx
|
|
|
|
|
subl %ecx,%edx
|
|
|
|
|
100: movb (%rsi),%al
|
|
|
|
|
101: movb %al,(%rdi)
|
|
|
|
|
incq %rsi
|
|
|
|
|
incq %rdi
|
|
|
|
|
decl %ecx
|
|
|
|
|
jnz 100b
|
|
|
|
|
102:
|
|
|
|
|
.section .fixup,"ax"
|
|
|
|
|
103: addl %ecx,%edx /* ecx is zerorest also */
|
|
|
|
|
jmp copy_user_handle_tail
|
|
|
|
|
.previous
|
|
|
|
|
|
|
|
|
|
_ASM_EXTABLE(100b,103b)
|
|
|
|
|
_ASM_EXTABLE(101b,103b)
|
|
|
|
|
.endm
|
|
|
|
|
|
2009-08-31 18:57:20 +00:00
|
|
|
#else
|
2016-02-17 18:20:12 +00:00
|
|
|
# define _EXPAND_EXTABLE_HANDLE(x) #x
|
|
|
|
|
# define _ASM_EXTABLE_HANDLE(from, to, handler) \
|
2012-04-20 23:57:35 +00:00
|
|
|
" .pushsection \"__ex_table\",\"a\"\n" \
|
2016-02-17 18:20:12 +00:00
|
|
|
" .balign 4\n" \
|
2012-04-21 00:12:48 +00:00
|
|
|
" .long (" #from ") - .\n" \
|
|
|
|
|
" .long (" #to ") - .\n" \
|
2016-02-17 18:20:12 +00:00
|
|
|
" .long (" _EXPAND_EXTABLE_HANDLE(handler) ") - .\n" \
|
2012-04-20 23:57:35 +00:00
|
|
|
" .popsection\n"
|
|
|
|
|
|
2016-02-17 18:20:12 +00:00
|
|
|
# define _ASM_EXTABLE(from, to) \
|
|
|
|
|
_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
|
|
|
|
|
|
|
|
|
|
# define _ASM_EXTABLE_FAULT(from, to) \
|
|
|
|
|
_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
|
|
|
|
|
|
|
|
|
|
# define _ASM_EXTABLE_EX(from, to) \
|
|
|
|
|
_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
|
|
|
|
|
|
locking/refcounts, x86/asm: Implement fast refcount overflow protection
This implements refcount_t overflow protection on x86 without a noticeable
performance impact, though without the fuller checking of REFCOUNT_FULL.
This is done by duplicating the existing atomic_t refcount implementation
but with normally a single instruction added to detect if the refcount
has gone negative (e.g. wrapped past INT_MAX or below zero). When detected,
the handler saturates the refcount_t to INT_MIN / 2. With this overflow
protection, the erroneous reference release that would follow a wrap back
to zero is blocked from happening, avoiding the class of refcount-overflow
use-after-free vulnerabilities entirely.
Only the overflow case of refcounting can be perfectly protected, since
it can be detected and stopped before the reference is freed and left to
be abused by an attacker. There isn't a way to block early decrements,
and while REFCOUNT_FULL stops increment-from-zero cases (which would
be the state _after_ an early decrement and stops potential double-free
conditions), this fast implementation does not, since it would require
the more expensive cmpxchg loops. Since the overflow case is much more
common (e.g. missing a "put" during an error path), this protection
provides real-world protection. For example, the two public refcount
overflow use-after-free exploits published in 2016 would have been
rendered unexploitable:
http://perception-point.io/2016/01/14/analysis-and-exploitation-of-a-linux-kernel-vulnerability-cve-2016-0728/
http://cyseclabs.com/page?n=02012016
This implementation does, however, notice an unchecked decrement to zero
(i.e. caller used refcount_dec() instead of refcount_dec_and_test() and it
resulted in a zero). Decrements under zero are noticed (since they will
have resulted in a negative value), though this only indicates that a
use-after-free may have already happened. Such notifications are likely
avoidable by an attacker that has already exploited a use-after-free
vulnerability, but it's better to have them reported than allow such
conditions to remain universally silent.
On first overflow detection, the refcount value is reset to INT_MIN / 2
(which serves as a saturation value) and a report and stack trace are
produced. When operations detect only negative value results (such as
changing an already saturated value), saturation still happens but no
notification is performed (since the value was already saturated).
On the matter of races, since the entire range beyond INT_MAX but before
0 is negative, every operation at INT_MIN / 2 will trap, leaving no
overflow-only race condition.
As for performance, this implementation adds a single "js" instruction
to the regular execution flow of a copy of the standard atomic_t refcount
operations. (The non-"and_test" refcount_dec() function, which is uncommon
in regular refcount design patterns, has an additional "jz" instruction
to detect reaching exactly zero.) Since this is a forward jump, it is by
default the non-predicted path, which will be reinforced by dynamic branch
prediction. The result is this protection having virtually no measurable
change in performance over standard atomic_t operations. The error path,
located in .text.unlikely, saves the refcount location and then uses UD0
to fire a refcount exception handler, which resets the refcount, handles
reporting, and returns to regular execution. This keeps the changes to
.text size minimal, avoiding return jumps and open-coded calls to the
error reporting routine.
Example assembly comparison:
refcount_inc() before:
.text:
ffffffff81546149: f0 ff 45 f4 lock incl -0xc(%rbp)
refcount_inc() after:
.text:
ffffffff81546149: f0 ff 45 f4 lock incl -0xc(%rbp)
ffffffff8154614d: 0f 88 80 d5 17 00 js ffffffff816c36d3
...
.text.unlikely:
ffffffff816c36d3: 48 8d 4d f4 lea -0xc(%rbp),%rcx
ffffffff816c36d7: 0f ff (bad)
These are the cycle counts comparing a loop of refcount_inc() from 1
to INT_MAX and back down to 0 (via refcount_dec_and_test()), between
unprotected refcount_t (atomic_t), fully protected REFCOUNT_FULL
(refcount_t-full), and this overflow-protected refcount (refcount_t-fast):
2147483646 refcount_inc()s and 2147483647 refcount_dec_and_test()s:
cycles protections
atomic_t 82249267387 none
refcount_t-fast 82211446892 overflow, untested dec-to-zero
refcount_t-full 144814735193 overflow, untested dec-to-zero, inc-from-zero
This code is a modified version of the x86 PAX_REFCOUNT atomic_t
overflow defense from the last public patch of PaX/grsecurity, based
on my understanding of the code. Changes or omissions from the original
code are mine and don't reflect the original grsecurity/PaX code. Thanks
to PaX Team for various suggestions for improvement for repurposing this
code to be a refcount-only protection.
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Hans Liljestrand <ishkamiel@gmail.com>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: Jann Horn <jannh@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: arozansk@redhat.com
Cc: axboe@kernel.dk
Cc: kernel-hardening@lists.openwall.com
Cc: linux-arch <linux-arch@vger.kernel.org>
Link: http://lkml.kernel.org/r/20170815161924.GA133115@beast
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-08-15 16:19:24 +00:00
|
|
|
# define _ASM_EXTABLE_REFCOUNT(from, to) \
|
|
|
|
|
_ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
|
|
|
|
|
|
2014-04-17 08:17:05 +00:00
|
|
|
/* For C file, we already have NOKPROBE_SYMBOL macro */
|
2009-08-31 18:57:20 +00:00
|
|
|
#endif
|
2008-02-04 15:47:56 +00:00
|
|
|
|
x86/asm: Fix inline asm call constraints for Clang
For inline asm statements which have a CALL instruction, we list the
stack pointer as a constraint to convince GCC to ensure the frame
pointer is set up first:
static inline void foo()
{
register void *__sp asm(_ASM_SP);
asm("call bar" : "+r" (__sp))
}
Unfortunately, that pattern causes Clang to corrupt the stack pointer.
The fix is easy: convert the stack pointer register variable to a global
variable.
It should be noted that the end result is different based on the GCC
version. With GCC 6.4, this patch has exactly the same result as
before:
defconfig defconfig-nofp distro distro-nofp
before 9820389 9491555 8816046 8516940
after 9820389 9491555 8816046 8516940
With GCC 7.2, however, GCC's behavior has changed. It now changes its
behavior based on the conversion of the register variable to a global.
That somehow convinces it to *always* set up the frame pointer before
inserting *any* inline asm. (Therefore, listing the variable as an
output constraint is a no-op and is no longer necessary.) It's a bit
overkill, but the performance impact should be negligible. And in fact,
there's a nice improvement with frame pointers disabled:
defconfig defconfig-nofp distro distro-nofp
before 9796316 9468236 9076191 8790305
after 9796957 9464267 9076381 8785949
So in summary, while listing the stack pointer as an output constraint
is no longer necessary for newer versions of GCC, it's still needed for
older versions.
Suggested-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reported-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/3db862e970c432ae823cf515c52b54fec8270e0e.1505942196.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-20 21:24:33 +00:00
|
|
|
#ifndef __ASSEMBLY__
|
|
|
|
|
/*
|
|
|
|
|
* This output constraint should be used for any inline asm which has a "call"
|
|
|
|
|
* instruction. Otherwise the asm may be inserted before the frame pointer
|
|
|
|
|
* gets set up by the containing function. If you forget to do this, objtool
|
|
|
|
|
* may print a "call without frame pointer save/setup" warning.
|
|
|
|
|
*/
|
2017-09-29 14:15:36 +00:00
|
|
|
register unsigned long current_stack_pointer asm(_ASM_SP);
|
|
|
|
|
#define ASM_CALL_CONSTRAINT "+r" (current_stack_pointer)
|
x86/asm: Fix inline asm call constraints for Clang
For inline asm statements which have a CALL instruction, we list the
stack pointer as a constraint to convince GCC to ensure the frame
pointer is set up first:
static inline void foo()
{
register void *__sp asm(_ASM_SP);
asm("call bar" : "+r" (__sp))
}
Unfortunately, that pattern causes Clang to corrupt the stack pointer.
The fix is easy: convert the stack pointer register variable to a global
variable.
It should be noted that the end result is different based on the GCC
version. With GCC 6.4, this patch has exactly the same result as
before:
defconfig defconfig-nofp distro distro-nofp
before 9820389 9491555 8816046 8516940
after 9820389 9491555 8816046 8516940
With GCC 7.2, however, GCC's behavior has changed. It now changes its
behavior based on the conversion of the register variable to a global.
That somehow convinces it to *always* set up the frame pointer before
inserting *any* inline asm. (Therefore, listing the variable as an
output constraint is a no-op and is no longer necessary.) It's a bit
overkill, but the performance impact should be negligible. And in fact,
there's a nice improvement with frame pointers disabled:
defconfig defconfig-nofp distro distro-nofp
before 9796316 9468236 9076191 8790305
after 9796957 9464267 9076381 8785949
So in summary, while listing the stack pointer as an output constraint
is no longer necessary for newer versions of GCC, it's still needed for
older versions.
Suggested-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reported-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/3db862e970c432ae823cf515c52b54fec8270e0e.1505942196.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-20 21:24:33 +00:00
|
|
|
#endif
|
|
|
|
|
|
2008-10-23 05:26:29 +00:00
|
|
|
#endif /* _ASM_X86_ASM_H */
|
