forked from Minki/linux
6b32c126d3
The alt_max_short() macro in asm/alternative.h does not work as
intended, leading to nasty bugs. E.g. alt_max_short("1", "3")
evaluates to 3, but alt_max_short("3", "1") evaluates to 1 -- not
exactly the maximum of 1 and 3.
In fact, I had to learn it the hard way by crashing my kernel in not
so funny ways by attempting to make use of the ALTENATIVE_2 macro
with alternatives where the first one was larger than the second
one.
According to [1] and commit dbe4058a6a ("x86/alternatives: Fix
ALTERNATIVE_2 padding generation properly") the right handed side
should read "-(-(a < b))" not "-(-(a - b))". Fix that, to make the
macro work as intended.
While at it, fix up the comments regarding the additional "-", too.
It's not about gas' usage of s32 but brain dead logic of having a
"true" value of -1 for the < operator ... *sigh*
Btw., the one in asm/alternative-asm.h is correct. And, apparently,
all current users of ALTERNATIVE_2() pass same sized alternatives,
avoiding to hit the bug.
[1] http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
Reviewed-and-tested-by: Borislav Petkov <bp@suse.de>
Fixes: dbe4058a6a ("x86/alternatives: Fix ALTERNATIVE_2 padding generation properly")
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1507228213-13095-1-git-send-email-minipli@googlemail.com
243 lines
8.3 KiB
C
243 lines
8.3 KiB
C
#ifndef _ASM_X86_ALTERNATIVE_H
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#define _ASM_X86_ALTERNATIVE_H
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#ifndef __ASSEMBLY__
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#include <linux/types.h>
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#include <linux/stddef.h>
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#include <linux/stringify.h>
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#include <asm/asm.h>
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/*
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* Alternative inline assembly for SMP.
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*
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* The LOCK_PREFIX macro defined here replaces the LOCK and
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* LOCK_PREFIX macros used everywhere in the source tree.
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*
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* SMP alternatives use the same data structures as the other
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* alternatives and the X86_FEATURE_UP flag to indicate the case of a
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* UP system running a SMP kernel. The existing apply_alternatives()
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* works fine for patching a SMP kernel for UP.
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*
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* The SMP alternative tables can be kept after boot and contain both
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* UP and SMP versions of the instructions to allow switching back to
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* SMP at runtime, when hotplugging in a new CPU, which is especially
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* useful in virtualized environments.
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*
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* The very common lock prefix is handled as special case in a
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* separate table which is a pure address list without replacement ptr
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* and size information. That keeps the table sizes small.
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*/
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#ifdef CONFIG_SMP
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#define LOCK_PREFIX_HERE \
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".pushsection .smp_locks,\"a\"\n" \
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".balign 4\n" \
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".long 671f - .\n" /* offset */ \
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".popsection\n" \
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"671:"
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#define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
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#else /* ! CONFIG_SMP */
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#define LOCK_PREFIX_HERE ""
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#define LOCK_PREFIX ""
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#endif
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struct alt_instr {
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s32 instr_offset; /* original instruction */
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s32 repl_offset; /* offset to replacement instruction */
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u16 cpuid; /* cpuid bit set for replacement */
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u8 instrlen; /* length of original instruction */
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u8 replacementlen; /* length of new instruction */
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u8 padlen; /* length of build-time padding */
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} __packed;
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/*
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* Debug flag that can be tested to see whether alternative
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* instructions were patched in already:
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*/
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extern int alternatives_patched;
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extern void alternative_instructions(void);
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extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
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struct module;
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#ifdef CONFIG_SMP
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extern void alternatives_smp_module_add(struct module *mod, char *name,
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void *locks, void *locks_end,
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void *text, void *text_end);
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extern void alternatives_smp_module_del(struct module *mod);
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extern void alternatives_enable_smp(void);
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extern int alternatives_text_reserved(void *start, void *end);
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extern bool skip_smp_alternatives;
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#else
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static inline void alternatives_smp_module_add(struct module *mod, char *name,
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void *locks, void *locks_end,
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void *text, void *text_end) {}
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static inline void alternatives_smp_module_del(struct module *mod) {}
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static inline void alternatives_enable_smp(void) {}
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static inline int alternatives_text_reserved(void *start, void *end)
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{
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return 0;
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}
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#endif /* CONFIG_SMP */
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#define b_replacement(num) "664"#num
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#define e_replacement(num) "665"#num
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#define alt_end_marker "663"
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#define alt_slen "662b-661b"
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#define alt_pad_len alt_end_marker"b-662b"
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#define alt_total_slen alt_end_marker"b-661b"
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#define alt_rlen(num) e_replacement(num)"f-"b_replacement(num)"f"
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#define __OLDINSTR(oldinstr, num) \
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"661:\n\t" oldinstr "\n662:\n" \
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".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * " \
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"((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"
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#define OLDINSTR(oldinstr, num) \
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__OLDINSTR(oldinstr, num) \
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alt_end_marker ":\n"
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/*
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* gas compatible max based on the idea from:
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* http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
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*
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* The additional "-" is needed because gas uses a "true" value of -1.
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*/
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#define alt_max_short(a, b) "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
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/*
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* Pad the second replacement alternative with additional NOPs if it is
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* additionally longer than the first replacement alternative.
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*/
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#define OLDINSTR_2(oldinstr, num1, num2) \
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"661:\n\t" oldinstr "\n662:\n" \
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".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * " \
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"(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n" \
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alt_end_marker ":\n"
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#define ALTINSTR_ENTRY(feature, num) \
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" .long 661b - .\n" /* label */ \
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" .long " b_replacement(num)"f - .\n" /* new instruction */ \
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" .word " __stringify(feature) "\n" /* feature bit */ \
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" .byte " alt_total_slen "\n" /* source len */ \
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" .byte " alt_rlen(num) "\n" /* replacement len */ \
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" .byte " alt_pad_len "\n" /* pad len */
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#define ALTINSTR_REPLACEMENT(newinstr, feature, num) /* replacement */ \
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b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"
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/* alternative assembly primitive: */
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#define ALTERNATIVE(oldinstr, newinstr, feature) \
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OLDINSTR(oldinstr, 1) \
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".pushsection .altinstructions,\"a\"\n" \
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ALTINSTR_ENTRY(feature, 1) \
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".popsection\n" \
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".pushsection .altinstr_replacement, \"ax\"\n" \
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ALTINSTR_REPLACEMENT(newinstr, feature, 1) \
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".popsection"
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#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
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OLDINSTR_2(oldinstr, 1, 2) \
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".pushsection .altinstructions,\"a\"\n" \
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ALTINSTR_ENTRY(feature1, 1) \
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ALTINSTR_ENTRY(feature2, 2) \
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".popsection\n" \
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".pushsection .altinstr_replacement, \"ax\"\n" \
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ALTINSTR_REPLACEMENT(newinstr1, feature1, 1) \
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ALTINSTR_REPLACEMENT(newinstr2, feature2, 2) \
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".popsection"
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/*
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* Alternative instructions for different CPU types or capabilities.
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*
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* This allows to use optimized instructions even on generic binary
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* kernels.
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*
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* length of oldinstr must be longer or equal the length of newinstr
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* It can be padded with nops as needed.
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*
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* For non barrier like inlines please define new variants
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* without volatile and memory clobber.
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*/
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#define alternative(oldinstr, newinstr, feature) \
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asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
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#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
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asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
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/*
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* Alternative inline assembly with input.
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*
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* Pecularities:
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* No memory clobber here.
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* Argument numbers start with 1.
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* Best is to use constraints that are fixed size (like (%1) ... "r")
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* If you use variable sized constraints like "m" or "g" in the
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* replacement make sure to pad to the worst case length.
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* Leaving an unused argument 0 to keep API compatibility.
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*/
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#define alternative_input(oldinstr, newinstr, feature, input...) \
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asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
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: : "i" (0), ## input)
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/*
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* This is similar to alternative_input. But it has two features and
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* respective instructions.
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*
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* If CPU has feature2, newinstr2 is used.
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* Otherwise, if CPU has feature1, newinstr1 is used.
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* Otherwise, oldinstr is used.
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*/
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#define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2, \
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feature2, input...) \
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asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, \
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newinstr2, feature2) \
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: : "i" (0), ## input)
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/* Like alternative_input, but with a single output argument */
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#define alternative_io(oldinstr, newinstr, feature, output, input...) \
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asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
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: output : "i" (0), ## input)
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/* Like alternative_io, but for replacing a direct call with another one. */
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#define alternative_call(oldfunc, newfunc, feature, output, input...) \
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asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
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: output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
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/*
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* Like alternative_call, but there are two features and respective functions.
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* If CPU has feature2, function2 is used.
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* Otherwise, if CPU has feature1, function1 is used.
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* Otherwise, old function is used.
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*/
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#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2, \
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output, input...) \
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{ \
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asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
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"call %P[new2]", feature2) \
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: output, ASM_CALL_CONSTRAINT \
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: [old] "i" (oldfunc), [new1] "i" (newfunc1), \
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[new2] "i" (newfunc2), ## input); \
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}
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/*
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* use this macro(s) if you need more than one output parameter
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* in alternative_io
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*/
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#define ASM_OUTPUT2(a...) a
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/*
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* use this macro if you need clobbers but no inputs in
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* alternative_{input,io,call}()
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*/
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#define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_X86_ALTERNATIVE_H */
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