[ 3.8.y.z extended stable ] Patch "Introduce [compat_]save_altstack_ex() to unbreak x86 SMAP" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    Introduce [compat_]save_altstack_ex() to unbreak x86 SMAP

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 06312f272ecac443a99b618d3e61737b078453e8 Mon Sep 17 00:00:00 2001
From: Al Viro <viro at ZenIV.linux.org.uk>
Date: Sun, 1 Sep 2013 20:35:01 +0100
Subject: Introduce [compat_]save_altstack_ex() to unbreak x86 SMAP

commit bd1c149aa9915b9abb6d83d0f01dfd2ace0680b5 upstream.

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 at linux.intel.com>
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>
Link: http://lkml.kernel.org/n/tip-es5p6y64if71k8p5u08agv9n@git.kernel.org
[ kamal: backport to 3.8 (context) ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/ia32/ia32_signal.c | 2 +-
 arch/x86/kernel/signal.c    | 6 +++---
 include/linux/compat.h      | 7 +++++++
 include/linux/signal.h      | 8 ++++++++
 4 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index a1daf4a..fb53906 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -467,7 +467,7 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 		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 (ka->sa.sa_flags & SA_RESTORER)
 			restorer = ka->sa.sa_restorer;
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index d6bf1f3..1697f73 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -364,7 +364,7 @@ static int __setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 		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);
@@ -429,7 +429,7 @@ static int __setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 		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.  */
@@ -496,7 +496,7 @@ static int x32_setup_rt_frame(int sig, struct k_sigaction *ka,
 		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 (ka->sa.sa_flags & SA_RESTORER) {
diff --git a/include/linux/compat.h b/include/linux/compat.h
index dec7e2d..98ac3c5 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -648,6 +648,13 @@ 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);
 #endif

 asmlinkage long compat_sys_sched_rr_get_interval(compat_pid_t pid,
diff --git a/include/linux/signal.h b/include/linux/signal.h
index 0a89ffc..b50aa60 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -388,4 +388,12 @@ 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);
+
 #endif /* _LINUX_SIGNAL_H */
--
1.8.1.2