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Subject[tip:x86/syscall] arm64/syscalls: Check address limit on user-mode return
Commit-ID:  cf7de27ab35172a9240f079477cae3146a182998
Gitweb: http://git.kernel.org/tip/cf7de27ab35172a9240f079477cae3146a182998
Author: Thomas Garnier <thgarnie@google.com>
AuthorDate: Wed, 14 Jun 2017 18:12:03 -0700
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 8 Jul 2017 14:05:33 +0200

arm64/syscalls: Check address limit on user-mode return

Ensure the address limit is a user-mode segment before returning to
user-mode. Otherwise a process can corrupt kernel-mode memory and
elevate privileges [1].

The set_fs function sets the TIF_SETFS flag to force a slow path on
return. In the slow path, the address limit is checked to be USER_DS if
needed.

[1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990

Signed-off-by: Thomas Garnier <thgarnie@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: kernel-hardening@lists.openwall.com
Cc: Will Deacon <will.deacon@arm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Will Drewry <wad@chromium.org>
Cc: linux-api@vger.kernel.org
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Link: http://lkml.kernel.org/r/20170615011203.144108-3-thgarnie@google.com

---
arch/arm64/include/asm/thread_info.h | 4 +++-
arch/arm64/include/asm/uaccess.h | 3 +++
arch/arm64/kernel/signal.c | 5 +++++
3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 46c3b93..c5ba565 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -86,6 +86,7 @@ struct thread_info {
#define TIF_NOTIFY_RESUME 2 /* callback before returning to user */
#define TIF_FOREIGN_FPSTATE 3 /* CPU's FP state is not current's */
#define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */
+#define TIF_FSCHECK 5 /* Check FS is USER_DS on return */
#define TIF_NOHZ 7
#define TIF_SYSCALL_TRACE 8
#define TIF_SYSCALL_AUDIT 9
@@ -107,11 +108,12 @@ struct thread_info {
#define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
#define _TIF_SECCOMP (1 << TIF_SECCOMP)
#define _TIF_UPROBE (1 << TIF_UPROBE)
+#define _TIF_FSCHECK (1 << TIF_FSCHECK)
#define _TIF_32BIT (1 << TIF_32BIT)

#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
_TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
- _TIF_UPROBE)
+ _TIF_UPROBE | _TIF_FSCHECK)

#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 7b8a047..ced7a7c 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -45,6 +45,9 @@ static inline void set_fs(mm_segment_t fs)
{
current_thread_info()->addr_limit = fs;

+ /* On user-mode return, check fs is correct */
+ set_thread_flag(TIF_FSCHECK);
+
/*
* Enable/disable UAO so that copy_to_user() etc can access
* kernel memory with the unprivileged instructions.
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index c7b6de6..0f02791 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -25,6 +25,7 @@
#include <linux/uaccess.h>
#include <linux/tracehook.h>
#include <linux/ratelimit.h>
+#include <linux/syscalls.h>

#include <asm/debug-monitors.h>
#include <asm/elf.h>
@@ -408,6 +409,10 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
* Update the trace code with the current status.
*/
trace_hardirqs_off();
+
+ /* Check valid user FS if needed */
+ addr_limit_user_check();
+
do {
if (thread_flags & _TIF_NEED_RESCHED) {
schedule();
\
 
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