Commit 0a4bb5e5 authored by Arvind Sankar's avatar Arvind Sankar Committed by Borislav Petkov
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x86/fpu: Allow multiple bits in clearcpuid= parameter 



Commit

  0c2a3913 ("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: 0c2a3913 ("x86/fpu: Parse clearcpuid= as early XSAVE argument")
Signed-off-by: default avatarArvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907213919.2423441-1-nivedita@alum.mit.edu
parent f4d51dff

Documentation/admin-guide/kernel-parameters.txt

+1 −1
Original line number Diff line number Diff line
@@ -577,7 +577,7 @@ 
			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

arch/x86/kernel/fpu/init.c

+22 −8
Original line number Diff line number Diff line
@@ -243,9 +243,9 @@ 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"))
@@ -268,13 +268,27 @@ 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)

	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");

}



/*

 * Called on the boot CPU once per system bootup, to set up the initial

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