This is a note to let you know that I've just added the patch titled x86/fpu: Allow multiple bits in clearcpuid= parameter to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-fpu-allow-multiple-bits-in-clearcpuid-parameter.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 0d1d35198a6286b70206ef821520b497c5cd1085 Author: Arvind Sankar <nivedita@xxxxxxxxxxxx> Date: Mon Sep 7 17:39:19 2020 -0400 x86/fpu: Allow multiple bits in clearcpuid= parameter [ 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@xxxxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Link: https://lkml.kernel.org/r/20200907213919.2423441-1-nivedita@xxxxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 30752db575870..fb129272240c9 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -558,7 +558,7 @@ 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 6abd83572b016..9692ccc583bb3 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -249,9 +249,9 @@ 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; if (cmdline_find_option_bool(boot_command_line, "no387")) setup_clear_cpu_cap(X86_FEATURE_FPU); @@ -271,12 +271,26 @@ 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"); } /*