From: Arvind Sankar nivedita@alum.mit.edu
[ Upstream commit 0a4bb5e5507a585532cc413125b921c8546fc39f ]
Commit
0c2a3913d6f5 ("x86/fpu: Parse clearcpuid= as early XSAVE argument")
changed clearcpuid parsing from __setup() to cmdline_find_option(). While the __setup() function would have been called for each clearcpuid= parameter on the command line, cmdline_find_option() will only return the last one, so the change effectively made it impossible to disable more than one bit.
Allow a comma-separated list of bit numbers as the argument for clearcpuid to allow multiple bits to be disabled again. Log the bits being disabled for informational purposes.
Also fix the check on the return value of cmdline_find_option(). It returns -1 when the option is not found, so testing as a boolean is incorrect.
Fixes: 0c2a3913d6f5 ("x86/fpu: Parse clearcpuid= as early XSAVE argument") Signed-off-by: Arvind Sankar nivedita@alum.mit.edu Signed-off-by: Borislav Petkov bp@suse.de Link: https://lkml.kernel.org/r/20200907213919.2423441-1-nivedita@alum.mit.edu Signed-off-by: Sasha Levin sashal@kernel.org --- .../admin-guide/kernel-parameters.txt | 2 +- arch/x86/kernel/fpu/init.c | 30 ++++++++++++++----- 2 files changed, 23 insertions(+), 9 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 13984b6cc3225..988a0d2535b25 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -567,7 +567,7 @@ loops can be debugged more effectively on production systems.
- clearcpuid=BITNUM [X86] + clearcpuid=BITNUM[,BITNUM...] [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 diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c index 6ce7e0a23268f..b271da0fa2193 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -242,9 +242,9 @@ static void __init fpu__init_system_ctx_switch(void) */ static void __init fpu__init_parse_early_param(void) { - char arg[32]; + char arg[128]; char *argptr = arg; - int bit; + int arglen, res, bit;
#ifdef CONFIG_X86_32 if (cmdline_find_option_bool(boot_command_line, "no387")) @@ -267,12 +267,26 @@ static void __init fpu__init_parse_early_param(void) if (cmdline_find_option_bool(boot_command_line, "noxsaves")) setup_clear_cpu_cap(X86_FEATURE_XSAVES);
- if (cmdline_find_option(boot_command_line, "clearcpuid", arg, - sizeof(arg)) && - get_option(&argptr, &bit) && - bit >= 0 && - bit < NCAPINTS * 32) - setup_clear_cpu_cap(bit); + arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg)); + if (arglen <= 0) + 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; + + if (bit >= 0 && bit < NCAPINTS * 32) { + pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit)); + setup_clear_cpu_cap(bit); + } + } while (res == 2); + pr_cont("\n"); }
/*