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| author | Andi Kleen <ak@linux.intel.com> | 2020-05-28 16:13:59 -0400 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-06-18 15:47:05 +0200 |
| commit | 742c45c3ecc9255e15eddbbcee44fd8de401cf1c (patch) | |
| tree | f97f2df3fdcd3de342e7231823da20078a194a85 /arch/x86/kernel/cpu/common.c | |
| parent | b745cfba44c152c34363eea9e052367b6b1d652b (diff) | |
| download | linux-742c45c3ecc9255e15eddbbcee44fd8de401cf1c.tar.bz2 | |
x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2
The kernel needs to explicitly enable FSGSBASE. So, the application needs
to know if it can safely use these instructions. Just looking at the CPUID
bit is not enough because it may be running in a kernel that does not
enable the instructions.
One way for the application would be to just try and catch the SIGILL.
But that is difficult to do in libraries which may not want to overwrite
the signal handlers of the main application.
Enumerate the enabled FSGSBASE capability in bit 1 of AT_HWCAP2 in the ELF
aux vector. AT_HWCAP2 is already used by PPC for similar purposes.
The application can access it open coded or by using the getauxval()
function in newer versions of glibc.
[ tglx: Massaged changelog ]
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1557309753-24073-18-git-send-email-chang.seok.bae@intel.com
Link: https://lkml.kernel.org/r/20200528201402.1708239-14-sashal@kernel.org
Diffstat (limited to 'arch/x86/kernel/cpu/common.c')
| -rw-r--r-- | arch/x86/kernel/cpu/common.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 18857ceb6bce..fca56129ddc7 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1512,8 +1512,10 @@ static void identify_cpu(struct cpuinfo_x86 *c) setup_umip(c); /* Enable FSGSBASE instructions if available. */ - if (cpu_has(c, X86_FEATURE_FSGSBASE)) + if (cpu_has(c, X86_FEATURE_FSGSBASE)) { cr4_set_bits(X86_CR4_FSGSBASE); + elf_hwcap2 |= HWCAP2_FSGSBASE; + } /* * The vendor-specific functions might have changed features. |