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Message-Id: <20170615011203.144108-3-thgarnie@google.com>
Date: Wed, 14 Jun 2017 18:12:03 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Rik van Riel <riel@...hat.com>,
Oleg Nesterov <oleg@...hat.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Thomas Garnier <thgarnie@...gle.com>,
Petr Mladek <pmladek@...e.com>,
Miroslav Benes <mbenes@...e.cz>,
Kees Cook <keescook@...omium.org>,
Al Viro <viro@...iv.linux.org.uk>,
Arnd Bergmann <arnd@...db.de>,
Dave Hansen <dave.hansen@...el.com>,
David Howells <dhowells@...hat.com>,
Russell King <linux@...linux.org.uk>,
Andy Lutomirski <luto@...capital.net>,
Will Drewry <wad@...omium.org>,
Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>,
Pratyush Anand <panand@...hat.com>,
Chris Metcalf <cmetcalf@...lanox.com>
Cc: x86@...nel.org,
linux-kernel@...r.kernel.org,
linux-api@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com
Subject: [PATCH v10 3/3] 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@...gle.com>
---
v10 redesigns the change to use work flags on set_fs as recommended by
Linus and agreed by others.
Based on next-20170609
---
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 46c3b93cf865..c5ba565544ee 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 7b8a04789cef..ced7a7c2dd41 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 c7b6de62f9d3..0f0279148bdc 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();
--
2.13.1.518.g3df882009-goog
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