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Commit bd1c149a authored Sep 01, 2013 by Al Viro Committed by H. Peter Anvin Sep 01, 2013

Introduce [compat_]save_altstack_ex() to unbreak x86 SMAP



For performance reasons, when SMAP is in use, SMAP is left open for an
entire put_user_try { ... } put_user_catch(); block, however, calling
__put_user() in the middle of that block will close SMAP as the
STAC..CLAC constructs intentionally do not nest.

Furthermore, using __put_user() rather than put_user_ex() here is bad
for performance.

Thus, introduce new [compat_]save_altstack_ex() helpers that replace
__[compat_]save_altstack() for x86, being currently the only
architecture which supports put_user_try { ... } put_user_catch().

Reported-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org> # v3.8+
Link: http://lkml.kernel.org/n/tip-es5p6y64if71k8p5u08agv9n@git.kernel.org

parent 7263dda4

arch/x86/ia32/ia32_signal.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -457,7 +457,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
	else		else
	put_user_ex(0, &frame->uc.uc_flags);		put_user_ex(0, &frame->uc.uc_flags);
	put_user_ex(0, &frame->uc.uc_link);		put_user_ex(0, &frame->uc.uc_link);
	err \|= __compat_save_altstack(&frame->uc.uc_stack, regs->sp);		compat_save_altstack_ex(&frame->uc.uc_stack, regs->sp);

	if (ksig->ka.sa.sa_flags & SA_RESTORER)		if (ksig->ka.sa.sa_flags & SA_RESTORER)
	restorer = ksig->ka.sa.sa_restorer;		restorer = ksig->ka.sa.sa_restorer;

arch/x86/kernel/signal.c

+3 −3

Original line number	Original line	Diff line number	Diff line
	@@ -358,7 +358,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
	else		else
	put_user_ex(0, &frame->uc.uc_flags);		put_user_ex(0, &frame->uc.uc_flags);
	put_user_ex(0, &frame->uc.uc_link);		put_user_ex(0, &frame->uc.uc_link);
	err \|= __save_altstack(&frame->uc.uc_stack, regs->sp);		save_altstack_ex(&frame->uc.uc_stack, regs->sp);

	/* Set up to return from userspace. */		/* Set up to return from userspace. */
	restorer = VDSO32_SYMBOL(current->mm->context.vdso, rt_sigreturn);		restorer = VDSO32_SYMBOL(current->mm->context.vdso, rt_sigreturn);
	@@ -423,7 +423,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
	else		else
	put_user_ex(0, &frame->uc.uc_flags);		put_user_ex(0, &frame->uc.uc_flags);
	put_user_ex(0, &frame->uc.uc_link);		put_user_ex(0, &frame->uc.uc_link);
	err \|= __save_altstack(&frame->uc.uc_stack, regs->sp);		save_altstack_ex(&frame->uc.uc_stack, regs->sp);

	/* Set up to return from userspace. If provided, use a stub		/* Set up to return from userspace. If provided, use a stub
	already in userspace. */		already in userspace. */
	@@ -490,7 +490,7 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
	else		else
	put_user_ex(0, &frame->uc.uc_flags);		put_user_ex(0, &frame->uc.uc_flags);
	put_user_ex(0, &frame->uc.uc_link);		put_user_ex(0, &frame->uc.uc_link);
	err \|= __compat_save_altstack(&frame->uc.uc_stack, regs->sp);		compat_save_altstack_ex(&frame->uc.uc_stack, regs->sp);
	put_user_ex(0, &frame->uc.uc__pad0);		put_user_ex(0, &frame->uc.uc__pad0);

	if (ksig->ka.sa.sa_flags & SA_RESTORER) {		if (ksig->ka.sa.sa_flags & SA_RESTORER) {

include/linux/compat.h

+7 −0

Original line number	Original line	Diff line number	Diff line
	@@ -669,6 +669,13 @@ asmlinkage long compat_sys_sigaltstack(const compat_stack_t __user *uss_ptr,

	int compat_restore_altstack(const compat_stack_t __user *uss);		int compat_restore_altstack(const compat_stack_t __user *uss);
	int __compat_save_altstack(compat_stack_t __user *, unsigned long);		int __compat_save_altstack(compat_stack_t __user *, unsigned long);
			#define compat_save_altstack_ex(uss, sp) do { \
			compat_stack_t __user *__uss = uss; \
			struct task_struct *t = current; \
			put_user_ex(ptr_to_compat((void __user *)t->sas_ss_sp), &__uss->ss_sp); \
			put_user_ex(sas_ss_flags(sp), &__uss->ss_flags); \
			put_user_ex(t->sas_ss_size, &__uss->ss_size); \
			} while (0);

	asmlinkage long compat_sys_sched_rr_get_interval(compat_pid_t pid,		asmlinkage long compat_sys_sched_rr_get_interval(compat_pid_t pid,
	struct compat_timespec __user *interval);		struct compat_timespec __user *interval);

include/linux/signal.h

+8 −0

Original line number	Original line	Diff line number	Diff line
	@@ -434,6 +434,14 @@ void signals_init(void);
	int restore_altstack(const stack_t __user *);		int restore_altstack(const stack_t __user *);
	int __save_altstack(stack_t __user *, unsigned long);		int __save_altstack(stack_t __user *, unsigned long);

			#define save_altstack_ex(uss, sp) do { \
			stack_t __user *__uss = uss; \
			struct task_struct *t = current; \
			put_user_ex((void __user *)t->sas_ss_sp, &__uss->ss_sp); \
			put_user_ex(sas_ss_flags(sp), &__uss->ss_flags); \
			put_user_ex(t->sas_ss_size, &__uss->ss_size); \
			} while (0);

	#ifdef CONFIG_PROC_FS		#ifdef CONFIG_PROC_FS
	struct seq_file;		struct seq_file;
	extern void render_sigset_t(struct seq_file , const char , sigset_t *);		extern void render_sigset_t(struct seq_file , const char , sigset_t *);