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| author | Borislav Petkov <bp@suse.de> | 2013-06-09 14:07:32 +0400 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2013-06-21 04:37:19 +0400 |
| commit | 5700f743b597951743da9c7d891d3989aac0486e (patch) | |
| tree | e0482b8bb6ec72bc1db19bcd853922efb97b36bc /arch/x86/include | |
| parent | c3b83598c1eeb1507603b461f5843ec2a49e3033 (diff) | |
| download | linux-5700f743b597951743da9c7d891d3989aac0486e.tar.xz | |
x86: Sanity-check static_cpu_has usage
static_cpu_has may be used only after alternatives have run. Before that
it always returns false if constant folding with __builtin_constant_p()
doesn't happen. And you don't want that.
This patch is the result of me debugging an issue where I overzealously
put static_cpu_has in code which executed before alternatives have run
and had to spend some time with scratching head and cursing at the
monitor.
So add a jump to a warning which screams loudly when we use this
function too early. The alternatives patch that check away in
conjunction with patching the rest of the kernel image.
[ hpa: factored this into its own configuration option. If we want to
have an overarching option, it should be an option which selects
other options, not as a group option in the source code. ]
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1370772454-6106-4-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/include')
| -rw-r--r-- | arch/x86/include/asm/cpufeature.h | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 043d61e66efc..252b28f1176a 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -356,15 +356,35 @@ extern const char * const x86_power_flags[32]; #endif /* CONFIG_X86_64 */ #if __GNUC__ >= 4 +extern void warn_pre_alternatives(void); + /* * Static testing of CPU features. Used the same as boot_cpu_has(). * These are only valid after alternatives have run, but will statically * patch the target code for additional performance. - * */ static __always_inline __pure bool __static_cpu_has(u16 bit) { #if __GNUC__ > 4 || __GNUC_MINOR__ >= 5 + +#ifdef CONFIG_X86_DEBUG_STATIC_CPU_HAS + /* + * Catch too early usage of this before alternatives + * have run. + */ + asm goto("1: jmp %l[t_warn]\n" + "2:\n" + ".section .altinstructions,\"a\"\n" + " .long 1b - .\n" + " .long 0\n" /* no replacement */ + " .word %P0\n" /* 1: do replace */ + " .byte 2b - 1b\n" /* source len */ + " .byte 0\n" /* replacement len */ + ".previous\n" + /* skipping size check since replacement size = 0 */ + : : "i" (X86_FEATURE_ALWAYS) : : t_warn); +#endif + asm goto("1: jmp %l[t_no]\n" "2:\n" ".section .altinstructions,\"a\"\n" @@ -379,7 +399,13 @@ static __always_inline __pure bool __static_cpu_has(u16 bit) return true; t_no: return false; -#else + +#ifdef CONFIG_X86_DEBUG_STATIC_CPU_HAS + t_warn: + warn_pre_alternatives(); + return false; +#endif +#else /* GCC_VERSION >= 40500 */ u8 flag; /* Open-coded due to __stringify() in ALTERNATIVE() */ asm volatile("1: movb $0,%0\n" |