Commit 87194efe authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'x86_fsgsbase_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull x86 fsgsbase updates from Borislav Petkov:
 "Misc minor cleanups and corrections to the fsgsbase code and
  respective selftests"

* tag 'x86_fsgsbase_for_v5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  selftests/x86/fsgsbase: Test PTRACE_PEEKUSER for GSBASE with invalid LDT GS
  selftests/x86/fsgsbase: Reap a forgotten child
  x86/fsgsbase: Replace static_cpu_has() with boot_cpu_has()
  x86/entry/64: Correct the comment over SAVE_AND_SET_GSBASE
parents 9e536c81 1b9abd17

arch/x86/entry/entry_64.S

+3 −2
Original line number Diff line number Diff line
@@ -842,8 +842,9 @@ SYM_CODE_START_LOCAL(paranoid_entry) 
	 * retrieve and set the current CPUs kernel GSBASE. The stored value

	 * has to be restored in paranoid_exit unconditionally.

	 *

	 * The MSR write ensures that no subsequent load is based on a

	 * mispredicted GSBASE. No extra FENCE required.

	 * The unconditional write to GS base below ensures that no subsequent

	 * loads based on a mispredicted GS base can happen, therefore no LFENCE

	 * is needed here.

	 */

	SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx

	ret

arch/x86/include/asm/fsgsbase.h

+2 −2
Original line number Diff line number Diff line
@@ -57,7 +57,7 @@ static inline unsigned long x86_fsbase_read_cpu(void) 
{

	unsigned long fsbase;



	if (static_cpu_has(X86_FEATURE_FSGSBASE))

	if (boot_cpu_has(X86_FEATURE_FSGSBASE))

		fsbase = rdfsbase();

	else

		rdmsrl(MSR_FS_BASE, fsbase);
@@ -67,7 +67,7 @@ static inline unsigned long x86_fsbase_read_cpu(void) 


static inline void x86_fsbase_write_cpu(unsigned long fsbase)

{

	if (static_cpu_has(X86_FEATURE_FSGSBASE))

	if (boot_cpu_has(X86_FEATURE_FSGSBASE))

		wrfsbase(fsbase);

	else

		wrmsrl(MSR_FS_BASE, fsbase);

arch/x86/kernel/process_64.c

+4 −4
Original line number Diff line number Diff line
@@ -407,7 +407,7 @@ unsigned long x86_gsbase_read_cpu_inactive(void) 
{

	unsigned long gsbase;



	if (static_cpu_has(X86_FEATURE_FSGSBASE)) {

	if (boot_cpu_has(X86_FEATURE_FSGSBASE)) {

		unsigned long flags;



		local_irq_save(flags);
@@ -422,7 +422,7 @@ unsigned long x86_gsbase_read_cpu_inactive(void) 


void x86_gsbase_write_cpu_inactive(unsigned long gsbase)

{

	if (static_cpu_has(X86_FEATURE_FSGSBASE)) {

	if (boot_cpu_has(X86_FEATURE_FSGSBASE)) {

		unsigned long flags;



		local_irq_save(flags);
@@ -439,7 +439,7 @@ unsigned long x86_fsbase_read_task(struct task_struct *task) 


	if (task == current)

		fsbase = x86_fsbase_read_cpu();

	else if (static_cpu_has(X86_FEATURE_FSGSBASE) ||

	else if (boot_cpu_has(X86_FEATURE_FSGSBASE) ||

		 (task->thread.fsindex == 0))

		fsbase = task->thread.fsbase;

	else
@@ -454,7 +454,7 @@ unsigned long x86_gsbase_read_task(struct task_struct *task) 


	if (task == current)

		gsbase = x86_gsbase_read_cpu_inactive();

	else if (static_cpu_has(X86_FEATURE_FSGSBASE) ||

	else if (boot_cpu_has(X86_FEATURE_FSGSBASE) ||

		 (task->thread.gsindex == 0))

		gsbase = task->thread.gsbase;

	else

tools/testing/selftests/x86/fsgsbase.c

+68 −0
Original line number Diff line number Diff line
@@ -443,6 +443,68 @@ static void test_unexpected_base(void) 


#define USER_REGS_OFFSET(r) offsetof(struct user_regs_struct, r)



static void test_ptrace_write_gs_read_base(void)

{

	int status;

	pid_t child = fork();



	if (child < 0)

		err(1, "fork");



	if (child == 0) {

		printf("[RUN]\tPTRACE_POKE GS, read GSBASE back\n");



		printf("[RUN]\tARCH_SET_GS to 1\n");

		if (syscall(SYS_arch_prctl, ARCH_SET_GS, 1) != 0)

			err(1, "ARCH_SET_GS");



		if (ptrace(PTRACE_TRACEME, 0, NULL, NULL) != 0)

			err(1, "PTRACE_TRACEME");



		raise(SIGTRAP);

		_exit(0);

	}



	wait(&status);



	if (WSTOPSIG(status) == SIGTRAP) {

		unsigned long base;

		unsigned long gs_offset = USER_REGS_OFFSET(gs);

		unsigned long base_offset = USER_REGS_OFFSET(gs_base);



		/* Read the initial base.  It should be 1. */

		base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL);

		if (base == 1) {

			printf("[OK]\tGSBASE started at 1\n");

		} else {

			nerrs++;

			printf("[FAIL]\tGSBASE started at 0x%lx\n", base);

		}



		printf("[RUN]\tSet GS = 0x7, read GSBASE\n");



		/* Poke an LDT selector into GS. */

		if (ptrace(PTRACE_POKEUSER, child, gs_offset, 0x7) != 0)

			err(1, "PTRACE_POKEUSER");



		/* And read the base. */

		base = ptrace(PTRACE_PEEKUSER, child, base_offset, NULL);



		if (base == 0 || base == 1) {

			printf("[OK]\tGSBASE reads as 0x%lx with invalid GS\n", base);

		} else {

			nerrs++;

			printf("[FAIL]\tGSBASE=0x%lx (should be 0 or 1)\n", base);

		}

	}



	ptrace(PTRACE_CONT, child, NULL, NULL);



	wait(&status);

	if (!WIFEXITED(status))

		printf("[WARN]\tChild didn't exit cleanly.\n");

}



static void test_ptrace_write_gsbase(void)

{

	int status;
@@ -517,6 +579,9 @@ static void test_ptrace_write_gsbase(void) 


END:

	ptrace(PTRACE_CONT, child, NULL, NULL);

	wait(&status);

	if (!WIFEXITED(status))

		printf("[WARN]\tChild didn't exit cleanly.\n");

}



int main()
@@ -526,6 +591,9 @@ int main() 
	shared_scratch = mmap(NULL, 4096, PROT_READ | PROT_WRITE,

			      MAP_ANONYMOUS | MAP_SHARED, -1, 0);



	/* Do these tests before we have an LDT. */

	test_ptrace_write_gs_read_base();



	/* Probe FSGSBASE */

	sethandler(SIGILL, sigill, 0);

	if (sigsetjmp(jmpbuf, 1) == 0) {

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