Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1607734 > unrolled thread

[PATCH v5 1/4] syscalls: Restore address limit after a syscall

Back to article view | Back to linux.kernel

Contents

  [PATCH v5 1/4] syscalls: Restore address limit after a syscall Thomas Garnier <thgarnie@google.com> - 2017-03-23 18:30 +0100
    [PATCH v5 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state Thomas Garnier <thgarnie@google.com> - 2017-03-23 18:30 +0100
      Re: [PATCH v5 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state Thomas Garnier <thgarnie@google.com> - 2017-03-23 21:40 +0100
    Re: [PATCH v5 1/4] syscalls: Restore address limit after a syscall Kees Cook <keescook@chromium.org> - 2017-03-23 21:20 +0100

#1607734 — [PATCH v5 1/4] syscalls: Restore address limit after a syscall

This patch ensures a syscall does not return to user-mode with a kernel
address limit. If that happened, a process can corrupt kernel-mode
memory and elevate privileges.

For example, it would mitigation this bug:

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

The CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE option is also
added so each architecture can optimize this change.

Signed-off-by: Thomas Garnier <thgarnie@google.com>
---
Based on next-20170322
---
 arch/s390/Kconfig        |  1 +
 include/linux/syscalls.h | 26 +++++++++++++++++++++++++-
 init/Kconfig             |  7 +++++++
 kernel/sys.c             |  7 +++++++
 4 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index a2dcef0aacc7..b73f5b87bc99 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -103,6 +103,7 @@ config S390
 	select ARCH_INLINE_WRITE_UNLOCK_BH
 	select ARCH_INLINE_WRITE_UNLOCK_IRQ
 	select ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
+	select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
 	select ARCH_SAVE_PAGE_KEYS if HIBERNATION
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_NUMA_BALANCING
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 980c3c9b06f8..f9ff80fa92ff 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -191,6 +191,27 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 	SYSCALL_METADATA(sname, x, __VA_ARGS__)			\
 	__SYSCALL_DEFINEx(x, sname, __VA_ARGS__)
 
+
+/*
+ * Called before coming back to user-mode. Returning to user-mode with an
+ * address limit different than USER_DS can allow to overwrite kernel memory.
+ */
+static inline void verify_pre_usermode_state(void) {
+	BUG_ON(!segment_eq(get_fs(), USER_DS));
+}
+
+#ifndef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
+#define __CHECK_USER_CALLER() \
+	bool user_caller = segment_eq(get_fs(), USER_DS)
+#define __VERIFY_PRE_USERMODE_STATE() \
+	if (user_caller) verify_pre_usermode_state()
+#else
+#define __CHECK_USER_CALLER()
+#define __VERIFY_PRE_USERMODE_STATE()
+asmlinkage void asm_verify_pre_usermode_state(void);
+#endif
+
+
 #define __PROTECT(...) asmlinkage_protect(__VA_ARGS__)
 #define __SYSCALL_DEFINEx(x, name, ...)					\
 	asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))	\
@@ -199,7 +220,10 @@ extern struct trace_event_functions exit_syscall_print_funcs;
 	asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__));	\
 	asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__))	\
 	{								\
-		long ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__));	\
+		long ret;						\
+		__CHECK_USER_CALLER();					\
+		ret = SYSC##name(__MAP(x,__SC_CAST,__VA_ARGS__));	\
+		__VERIFY_PRE_USERMODE_STATE();				\
 		__MAP(x,__SC_TEST,__VA_ARGS__);				\
 		__PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__));	\
 		return ret;						\
diff --git a/init/Kconfig b/init/Kconfig
index c859c993c26f..c4efc3a95e4a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1929,6 +1929,13 @@ config PROFILING
 config TRACEPOINTS
 	bool
 
+#
+# Set by each architecture that want to optimize how verify_pre_usermode_state
+# is called.
+#
+config ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
+	bool
+
 source "arch/Kconfig"
 
 endmenu		# General setup
diff --git a/kernel/sys.c b/kernel/sys.c
index 196c7134bee6..4ae278fcc290 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2459,3 +2459,10 @@ COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info)
 	return 0;
 }
 #endif /* CONFIG_COMPAT */
+
+#ifdef CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
+asmlinkage void asm_verify_pre_usermode_state(void)
+{
+	verify_pre_usermode_state();
+}
+#endif
-- 
2.12.1.500.gab5fba24ee-goog

[toc] | [next] | [standalone]

#1607736 — [PATCH v5 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state

Implement specific usage of verify_pre_usermode_state for user-mode
returns for arm64.
---
Based on next-20170322
---
 arch/arm64/Kconfig        |  1 +
 arch/arm64/kernel/entry.S | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f2b0b528037d..0e86d87259f4 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -24,6 +24,7 @@ config ARM64
 	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
+	select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
 	select ARM_AMBA
 	select ARM_ARCH_TIMER
 	select ARM_GIC
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 43512d4d7df2..6d598e7051c3 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -744,6 +744,10 @@ ENDPROC(cpu_switch_to)
 ret_fast_syscall:
 	disable_irq				// disable interrupts
 	str	x0, [sp, #S_X0]			// returned x0
+	ldr	x2, [tsk, #TSK_TI_ADDR_LIMIT]	// check addr limit change
+	mov	x1, #TASK_SIZE_64
+	cmp	x2, x1
+	b.ne	addr_limit_fail
 	ldr	x1, [tsk, #TSK_TI_FLAGS]	// re-check for syscall tracing
 	and	x2, x1, #_TIF_SYSCALL_WORK
 	cbnz	x2, ret_fast_syscall_trace
@@ -771,6 +775,11 @@ work_pending:
  */
 ret_to_user:
 	disable_irq				// disable interrupts
+	ldr	x2, [tsk, #TSK_TI_ADDR_LIMIT]	// check addr limit change
+	mov	x1, #TASK_SIZE_64
+	cmp	x2, x1
+	b.ne	addr_limit_fail
+
 	ldr	x1, [tsk, #TSK_TI_FLAGS]
 	and	x2, x1, #_TIF_WORK_MASK
 	cbnz	x2, work_pending
@@ -779,6 +788,12 @@ finish_ret_to_user:
 	kernel_exit 0
 ENDPROC(ret_to_user)
 
+addr_limit_fail:
+	stp	x0, lr, [sp,#-16]!
+	bl	asm_verify_pre_usermode_state
+	ldp	x0, lr, [sp],#16
+	ret	lr
+
 /*
  * This is how we return from a fork.
  */
-- 
2.12.1.500.gab5fba24ee-goog

[toc] | [prev] | [next] | [standalone]

#1607883 — Re: [PATCH v5 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state

On Thu, Mar 23, 2017 at 10:25 AM, Thomas Garnier <thgarnie@google.com> wrote:
> Implement specific usage of verify_pre_usermode_state for user-mode
> returns for arm64.

Signed-off-by: Thomas Garnier <thgarnie@google.com>

Not sure why it was not there anymore.

-- 
Thomas

[toc] | [prev] | [next] | [standalone]

#1607871

On Thu, Mar 23, 2017 at 10:25 AM, Thomas Garnier <thgarnie@google.com> wrote:
> This patch ensures a syscall does not return to user-mode with a kernel
> address limit. If that happened, a process can corrupt kernel-mode
> memory and elevate privileges.
>
> For example, it would mitigation this bug:
>
> - https://bugs.chromium.org/p/project-zero/issues/detail?id=990
>
> The CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE option is also
> added so each architecture can optimize this change.
>
> Signed-off-by: Thomas Garnier <thgarnie@google.com>

Awesome. :) I've tested this on x86 and arm with the LKDTM patch I'll
post in a moment.

[   46.977823] lkdtm: Performing direct entry CORRUPT_USER_DS
[   46.978966] lkdtm: setting bad task size limit
[   46.980302] ------------[ cut here ]------------
[   46.981219] kernel BUG at ./include/linux/syscalls.h:200!

Tested-by: Kees Cook <keescook@chromium.org>

(Also note, your Signed-off-by lines are missing in patches 2-4)

-- 
Kees Cook
Pixel Security

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web