2012-09-21 19:43:09 +00:00
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#ifndef _ASM_X86_ALTERNATIVE_ASM_H
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#define _ASM_X86_ALTERNATIVE_ASM_H
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2007-10-17 16:04:38 +00:00
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#ifdef __ASSEMBLY__
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2009-11-27 15:06:16 +00:00
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#include <asm/asm.h>
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2007-10-17 16:04:38 +00:00
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#ifdef CONFIG_SMP
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.macro LOCK_PREFIX
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2012-01-03 16:35:40 +00:00
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672: lock
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2012-09-21 19:43:08 +00:00
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.pushsection .smp_locks,"a"
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2010-04-21 15:08:14 +00:00
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.balign 4
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2012-01-03 16:35:40 +00:00
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.long 672b - .
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2012-09-21 19:43:08 +00:00
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.popsection
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2007-10-17 16:04:38 +00:00
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.endm
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#else
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.macro LOCK_PREFIX
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.endm
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#endif
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2015-04-04 14:40:45 +00:00
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/*
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* Issue one struct alt_instr descriptor entry (need to put it into
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* the section .altinstructions, see below). This entry contains
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* enough information for the alternatives patching code to patch an
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* instruction. See apply_alternatives().
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*/
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2014-12-27 09:41:52 +00:00
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.macro altinstruction_entry orig alt feature orig_len alt_len pad_len
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2011-07-13 13:24:10 +00:00
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.long \orig - .
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.long \alt - .
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2011-05-17 22:29:13 +00:00
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.word \feature
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.byte \orig_len
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.byte \alt_len
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2014-12-27 09:41:52 +00:00
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.byte \pad_len
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.endm
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2015-04-04 14:40:45 +00:00
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/*
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* Define an alternative between two instructions. If @feature is
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* present, early code in apply_alternatives() replaces @oldinstr with
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* @newinstr. ".skip" directive takes care of proper instruction padding
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* in case @newinstr is longer than @oldinstr.
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*/
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2014-12-27 09:41:52 +00:00
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.macro ALTERNATIVE oldinstr, newinstr, feature
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140:
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\oldinstr
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141:
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.skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90
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142:
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.pushsection .altinstructions,"a"
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altinstruction_entry 140b,143f,\feature,142b-140b,144f-143f,142b-141b
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.popsection
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.pushsection .altinstr_replacement,"ax"
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143:
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\newinstr
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144:
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.popsection
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.endm
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x86/alternatives: Fix ALTERNATIVE_2 padding generation properly
Quentin caught a corner case with the generation of instruction
padding in the ALTERNATIVE_2 macro: if len(orig_insn) <
len(alt1) < len(alt2), then not enough padding gets added and
that is not good(tm) as we could overwrite the beginning of the
next instruction.
Luckily, at the time of this writing, we don't have
ALTERNATIVE_2() invocations which have that problem and even if
we did, a simple fix would be to prepend the instructions with
enough prefixes so that that corner case doesn't happen.
However, best it would be if we fixed it properly. See below for
a simple, abstracted example of what we're doing.
So what we ended up doing is, we compute the
max(len(alt1), len(alt2)) - len(orig_insn)
and feed that value to the .skip gas directive. The max() cannot
have conditionals due to gas limitations, thus the fancy integer
math.
With this patch, all ALTERNATIVE_2 sites get padded correctly;
generating obscure test cases pass too:
#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
#define gen_skip(orig, alt1, alt2, marker) \
.skip -((alt_max_short(alt1, alt2) - (orig)) > 0) * \
(alt_max_short(alt1, alt2) - (orig)),marker
.pushsection .text, "ax"
.globl main
main:
gen_skip(1, 2, 4, 0x09)
gen_skip(4, 1, 2, 0x10)
...
.popsection
Thanks to Quentin for catching it and double-checking the fix!
Reported-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150404133443.GE21152@pd.tnic
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-04-04 13:34:43 +00:00
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#define old_len 141b-140b
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#define new_len1 144f-143f
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#define new_len2 145f-144f
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/*
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* max without conditionals. Idea adapted from:
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* http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
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*/
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#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
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2015-04-04 14:40:45 +00:00
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/*
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* Same as ALTERNATIVE macro above but for two alternatives. If CPU
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* has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
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* @feature2, it replaces @oldinstr with @feature2.
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*/
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2014-12-27 09:41:52 +00:00
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.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
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140:
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\oldinstr
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141:
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x86/alternatives: Fix ALTERNATIVE_2 padding generation properly
Quentin caught a corner case with the generation of instruction
padding in the ALTERNATIVE_2 macro: if len(orig_insn) <
len(alt1) < len(alt2), then not enough padding gets added and
that is not good(tm) as we could overwrite the beginning of the
next instruction.
Luckily, at the time of this writing, we don't have
ALTERNATIVE_2() invocations which have that problem and even if
we did, a simple fix would be to prepend the instructions with
enough prefixes so that that corner case doesn't happen.
However, best it would be if we fixed it properly. See below for
a simple, abstracted example of what we're doing.
So what we ended up doing is, we compute the
max(len(alt1), len(alt2)) - len(orig_insn)
and feed that value to the .skip gas directive. The max() cannot
have conditionals due to gas limitations, thus the fancy integer
math.
With this patch, all ALTERNATIVE_2 sites get padded correctly;
generating obscure test cases pass too:
#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
#define gen_skip(orig, alt1, alt2, marker) \
.skip -((alt_max_short(alt1, alt2) - (orig)) > 0) * \
(alt_max_short(alt1, alt2) - (orig)),marker
.pushsection .text, "ax"
.globl main
main:
gen_skip(1, 2, 4, 0x09)
gen_skip(4, 1, 2, 0x10)
...
.popsection
Thanks to Quentin for catching it and double-checking the fix!
Reported-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150404133443.GE21152@pd.tnic
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-04-04 13:34:43 +00:00
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.skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
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(alt_max_short(new_len1, new_len2) - (old_len)),0x90
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2014-12-27 09:41:52 +00:00
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142:
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.pushsection .altinstructions,"a"
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altinstruction_entry 140b,143f,\feature1,142b-140b,144f-143f,142b-141b
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altinstruction_entry 140b,144f,\feature2,142b-140b,145f-144f,142b-141b
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.popsection
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.pushsection .altinstr_replacement,"ax"
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143:
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\newinstr1
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144:
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\newinstr2
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145:
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.popsection
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2011-05-17 22:29:13 +00:00
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.endm
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2007-10-17 16:04:38 +00:00
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#endif /* __ASSEMBLY__ */
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2012-09-21 19:43:09 +00:00
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#endif /* _ASM_X86_ALTERNATIVE_ASM_H */
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