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Introduce [compat_]save_altstack_ex() to unbreak x86 SMAP

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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
This commit is contained in:
Al Viro 2013-09-01 20:35:01 +01:00 committed by H. Peter Anvin
parent 7263dda41b
commit bd1c149aa9
4 changed files with 19 additions and 4 deletions
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2
arch/x86/ia32/ia32_signal.c
View file

@ -457,7 +457,7 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
else
put_user_ex(0, &frame->uc.uc_flags);
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)
restorer = ksig->ka.sa.sa_restorer;

6
arch/x86/kernel/signal.c
View file

@ -358,7 +358,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
else
put_user_ex(0, &frame->uc.uc_flags);
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. */
restorer = VDSO32_SYMBOL(current->mm->context.vdso, rt_sigreturn);
@ -423,7 +423,7 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
else
put_user_ex(0, &frame->uc.uc_flags);
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
already in userspace. */
@ -490,7 +490,7 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
else
put_user_ex(0, &frame->uc.uc_flags);
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);
if (ksig->ka.sa.sa_flags & SA_RESTORER) {

7
include/linux/compat.h
View file

@ -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_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,
struct compat_timespec __user *interval);

8
include/linux/signal.h
View file

@ -434,6 +434,14 @@ void signals_init(void);
int restore_altstack(const stack_t __user *);
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
struct seq_file;
extern void render_sigset_t(struct seq_file *, const char *, sigset_t *);