Messages in this thread Patch in this message | | | Date | Tue, 25 Jan 2022 12:45:47 +0100 | From | Borislav Petkov <> | Subject | [PATCH v1.1] x86/cpu: Allow feature bit names from /proc/cpuinfo in clearcpuid= |
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On Fri, Nov 12, 2021 at 11:32:41AM +0100, Borislav Petkov wrote: > clearcpuid=de,440,smca,succory,bmi1,3dnow ("succory" is wrong on > purpose).
Here's v1.1 which handles the case where we have ""-defined feature flags - for example:
#define X86_FEATURE_AMD_SSBD (13*32+24) /* "" Speculative Store Bypass Disable */
and for which there's no string name generated.
--- From: Borislav Petkov <bp@suse.de> Date: Wed, 10 Nov 2021 19:30:07 +0100 Subject: [PATCH v1.1] 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:
[ 0.000000] Clearing CPUID bits: de 13:24 smca bmi1 3dnow
Signed-off-by: Borislav Petkov <bp@suse.de> Link: https://lore.kernel.org/r/20211112103246.7555-2-bp@alien8.de --- .../admin-guide/kernel-parameters.txt | 11 +++- arch/x86/include/asm/cpufeature.h | 7 ++- arch/x86/kernel/cpu/common.c | 57 +++++++++++++++---- 3 files changed, 58 insertions(+), 17 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f5a27f067db9..b67d0cf27997 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 diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 1261842d006c..66d3e3b1d24d 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -34,14 +34,17 @@ enum cpuid_leafs CPUID_8000_001F_EAX, }; +#define X86_CAP_FMT_NUM "%d:%d" +#define x86_cap_flag_num(flag) ((flag) >> 5), ((flag) & 31) + #ifdef CONFIG_X86_FEATURE_NAMES extern const char * const x86_cap_flags[NCAPINTS*32]; extern const char * const x86_power_flags[32]; #define X86_CAP_FMT "%s" #define x86_cap_flag(flag) x86_cap_flags[flag] #else -#define X86_CAP_FMT "%d:%d" -#define x86_cap_flag(flag) ((flag) >> 5), ((flag) & 31) +#define X86_CAP_FMT X86_CAP_FMT_NUM +#define x86_cap_flag x86_cap_flag_num #endif /* diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 7b8382c11788..aaac18d800a4 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1237,8 +1237,8 @@ static void detect_nopl(void) static void __init cpu_parse_early_param(void) { char arg[128]; - char *argptr = arg; - int arglen, res, bit; + char *argptr = arg, *opt; + int arglen, taint = 0; #ifdef CONFIG_X86_32 if (cmdline_find_option_bool(boot_command_line, "no387")) @@ -1266,21 +1266,54 @@ static void __init cpu_parse_early_param(void) return; pr_info("Clearing CPUID bits:"); - do { - res = get_option(&argptr, &bit); - if (res == 0 || res == 3) - break; - /* If the argument was too long, the last bit may be cut off */ - if (res == 1 && arglen >= sizeof(arg)) - break; + while (argptr) { + unsigned int bit; + + opt = strsep(&argptr, ","); - if (bit >= 0 && bit < NCAPINTS * 32) { - pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit)); + /* + * Handle naked numbers first for feature flags which don't + * have names. + */ + if (!kstrtouint(opt, 10, &bit)) { + if (bit < NCAPINTS * 32) { + + /* empty-string, i.e., ""-defined feature flags */ + if (!x86_cap_flags[bit]) + pr_cont(" " X86_CAP_FMT_NUM, x86_cap_flag_num(bit)); + else + pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit)); + + setup_clear_cpu_cap(bit); + taint++; + } + /* + * The assumption is that there are no feature names with only + * numbers in the name thus go to the next argument. + */ + continue; + } + +#ifdef CONFIG_X86_FEATURE_NAMES + for (bit = 0; bit < 32 * NCAPINTS; bit++) { + if (!x86_cap_flag(bit)) + continue; + + if (strcmp(x86_cap_flag(bit), opt)) + continue; + + pr_cont(" %s", opt); setup_clear_cpu_cap(bit); + taint++; + break; } - } while (res == 2); +#endif + } pr_cont("\n"); + + if (taint) + add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK); } /* -- 2.29.2 -- Regards/Gruss, Boris.
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