Commit 1ef5423a authored by Mike Hommey's avatar Mike Hommey Committed by Borislav Petkov
Browse files

x86/fpu: Handle FPU-related and clearcpuid command line arguments earlier 



FPU initialization handles them currently. However, in the case
of clearcpuid=, some other early initialization code may check for
features before the FPU initialization code is called. Handling the
argument earlier allows the command line to influence those early
initializations.

Signed-off-by: default avatarMike Hommey <mh@glandium.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200921215638.37980-1-mh@glandium.org
parent 0a4bb5e5

arch/x86/kernel/cpu/common.c

+55 −0
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 
#include <linux/syscore_ops.h>

#include <linux/pgtable.h>



#include <asm/cmdline.h>

#include <asm/stackprotector.h>

#include <asm/perf_event.h>

#include <asm/mmu_context.h>
@@ -1220,6 +1221,59 @@ static void detect_nopl(void) 
#endif

}



/*

 * We parse cpu parameters early because fpu__init_system() is executed

 * before parse_early_param().

 */

static void __init cpu_parse_early_param(void)

{

	char arg[128];

	char *argptr = arg;

	int arglen, res, bit;



#ifdef CONFIG_X86_32

	if (cmdline_find_option_bool(boot_command_line, "no387"))

#ifdef CONFIG_MATH_EMULATION

		setup_clear_cpu_cap(X86_FEATURE_FPU);

#else

		pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");

#endif



	if (cmdline_find_option_bool(boot_command_line, "nofxsr"))

		setup_clear_cpu_cap(X86_FEATURE_FXSR);

#endif



	if (cmdline_find_option_bool(boot_command_line, "noxsave"))

		setup_clear_cpu_cap(X86_FEATURE_XSAVE);



	if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))

		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);



	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))

		setup_clear_cpu_cap(X86_FEATURE_XSAVES);



	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");

}



/*

 * Do minimum CPU detection early.

 * Fields really needed: vendor, cpuid_level, family, model, mask,
@@ -1255,6 +1309,7 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c) 
		get_cpu_cap(c);

		get_cpu_address_sizes(c);

		setup_force_cpu_cap(X86_FEATURE_CPUID);

		cpu_parse_early_param();



		if (this_cpu->c_early_init)

			this_cpu->c_early_init(c);

arch/x86/kernel/fpu/init.c

+0 −55
Original line number Diff line number Diff line
@@ -5,7 +5,6 @@ 
#include <asm/fpu/internal.h>

#include <asm/tlbflush.h>

#include <asm/setup.h>

#include <asm/cmdline.h>



#include <linux/sched.h>

#include <linux/sched/task.h>
@@ -237,66 +236,12 @@ static void __init fpu__init_system_ctx_switch(void) 
	on_boot_cpu = 0;

}



/*

 * We parse fpu parameters early because fpu__init_system() is executed

 * before parse_early_param().

 */

static void __init fpu__init_parse_early_param(void)

{

	char arg[128];

	char *argptr = arg;

	int arglen, res, bit;



#ifdef CONFIG_X86_32

	if (cmdline_find_option_bool(boot_command_line, "no387"))

#ifdef CONFIG_MATH_EMULATION

		setup_clear_cpu_cap(X86_FEATURE_FPU);

#else

		pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");

#endif



	if (cmdline_find_option_bool(boot_command_line, "nofxsr"))

		setup_clear_cpu_cap(X86_FEATURE_FXSR);

#endif



	if (cmdline_find_option_bool(boot_command_line, "noxsave"))

		setup_clear_cpu_cap(X86_FEATURE_XSAVE);



	if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))

		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);



	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))

		setup_clear_cpu_cap(X86_FEATURE_XSAVES);



	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

 * FPU state that is later cloned into all processes:

 */

void __init fpu__init_system(struct cpuinfo_x86 *c)

{

	fpu__init_parse_early_param();

	fpu__init_system_early_generic(c);



	/*

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