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| author | Borislav Petkov <bp@suse.de> | 2022-01-27 14:56:21 +0300 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2022-04-04 11:16:52 +0300 |
| commit | 1625c833db93516faaac5feedadf8d19c14238b6 (patch) | |
| tree | cb6bfcfdbec0e67637e0cc00842c35637816051f /Documentation/admin-guide/kernel-parameters.txt | |
| parent | 3123109284176b1532874591f7c81f3837bbdc17 (diff) | |
| download | linux-1625c833db93516faaac5feedadf8d19c14238b6.tar.xz | |
x86/cpu: Allow feature bit names from /proc/cpuinfo in clearcpuid=
Having to give the X86_FEATURE array indices in order to disable a
feature bit for testing is not really user-friendly. So accept the
feature bit names too.
Some feature bits don't have names so there the array indices are still
accepted, of course.
Clearing CPUID flags is not something which should be done in production
so taint the kernel too.
An exemplary cmdline would then be something like:
clearcpuid=de,440,smca,succory,bmi1,3dnow
("succory" is wrong on purpose). And it says:
[ ... ] Clearing CPUID bits: de 13:24 smca (unknown: succory) bmi1 3dnow
[ Fix CONFIG_X86_FEATURE_NAMES=n build error as reported by the 0day
robot: https://lore.kernel.org/r/202203292206.ICsY2RKX-lkp@intel.com ]
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220127115626.14179-2-bp@alien8.de
Diffstat (limited to 'Documentation/admin-guide/kernel-parameters.txt')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 3f1cc5e317ed..0ea17869a089 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -631,12 +631,17 @@ Defaults to zero when built as a module and to 10 seconds when built into the kernel. - clearcpuid=BITNUM[,BITNUM...] [X86] + clearcpuid=X[,X...] [X86] Disable CPUID feature X for the kernel. See arch/x86/include/asm/cpufeatures.h for the valid bit - numbers. Note the Linux specific bits are not necessarily - stable over kernel options, but the vendor specific + numbers X. Note the Linux-specific bits are not necessarily + stable over kernel options, but the vendor-specific ones should be. + X can also be a string as appearing in the flags: line + in /proc/cpuinfo which does not have the above + instability issue. However, not all features have names + in /proc/cpuinfo. + Note that using this option will taint your kernel. Also note that user programs calling CPUID directly or using the feature without checking anything will still see it. This just prevents it from |