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Re: [PATCH 01/12] x86: Update vfork to pop shadow stack
On Tue, Jul 24, 2018 at 5:32 AM, Carlos O'Donell <carlos@redhat.com> wrote:
> On 07/24/2018 08:25 AM, H.J. Lu wrote:
>> On Mon, Jul 23, 2018 at 7:47 PM, Carlos O'Donell <carlos@redhat.com> wrote:
>>> On 07/21/2018 10:20 AM, H.J. Lu wrote:
>>>> Since we can't change return address on shadow stack, if shadow stack
>>>> is in use, we need to pop shadow stack and jump back to caller directly.
>>>>
>>>> * sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER):
>>>> Redefine if shadow stack is enabled.
>>>> (SYSCALL_ERROR_LABEL): Likewise.
>>>> (__vfork): Pop shadow stack and jump back to to caller directly
>>>> when shadow stack is in use.
>>>> * sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER):
>>>> Redefine if shadow stack is enabled.
>>>> (SYSCALL_ERROR_LABEL): Likewise.
>>>> (__vfork): Pop shadow stack and jump back to to caller directly
>>>> when shadow stack is in use.
>>>> ---
>>>> sysdeps/unix/sysv/linux/i386/vfork.S | 54 ++++++++++++++++++++++++++
>>>> sysdeps/unix/sysv/linux/x86_64/vfork.S | 35 +++++++++++++++++
>>>> 2 files changed, 89 insertions(+)
>>>
>>> OK with comment suggestion.
>>>
>>> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
>>>
>>
>> This is what I checked in.
>>
>> Thanks.
>>
>
> Wrong patch?
>
Oops. Here is the right one.
--
H.J.
From 3650e1d9284926be67e368707a9a2276fb77a167 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 24 Jul 2018 05:20:48 -0700
Subject: [PATCH] x86: Update vfork to pop shadow stack
The shadow stack prevents us from pushing the saved return PC onto
the stack and returning normally. Instead we pop the shadow stack
and return directly. This is the safest way to return and ensures
any stack manipulations done by the vfork'd child doesn't cause the
parent to terminate when CET is enabled.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
* sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER):
Redefine if shadow stack is enabled.
(SYSCALL_ERROR_LABEL): Likewise.
(__vfork): Pop shadow stack and jump back to to caller directly
when shadow stack is in use.
* sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER):
Redefine if shadow stack is enabled.
(SYSCALL_ERROR_LABEL): Likewise.
(__vfork): Pop shadow stack and jump back to to caller directly
when shadow stack is in use.
---
ChangeLog | 13 ++++++
sysdeps/unix/sysv/linux/i386/vfork.S | 57 ++++++++++++++++++++++++++
sysdeps/unix/sysv/linux/x86_64/vfork.S | 38 +++++++++++++++++
3 files changed, 108 insertions(+)
diff --git a/ChangeLog b/ChangeLog
index 2a1a53d9df..8b892eb686 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2018-07-24 H.J. Lu <hongjiu.lu@intel.com>
+
+ * sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER):
+ Redefine if shadow stack is enabled.
+ (SYSCALL_ERROR_LABEL): Likewise.
+ (__vfork): Pop shadow stack and jump back to to caller directly
+ when shadow stack is in use.
+ * sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER):
+ Redefine if shadow stack is enabled.
+ (SYSCALL_ERROR_LABEL): Likewise.
+ (__vfork): Pop shadow stack and jump back to to caller directly
+ when shadow stack is in use.
+
2018-07-24 H.J. Lu <hongjiu.lu@intel.com>
* sysdeps/x86_64/tst-quadmod1.S (func): Add endbr64 if IBT is
diff --git a/sysdeps/unix/sysv/linux/i386/vfork.S b/sysdeps/unix/sysv/linux/i386/vfork.S
index 8f40d02d09..ce6dbfac48 100644
--- a/sysdeps/unix/sysv/linux/i386/vfork.S
+++ b/sysdeps/unix/sysv/linux/i386/vfork.S
@@ -21,6 +21,38 @@
#include <bits/errno.h>
#include <tcb-offsets.h>
+#if SHSTK_ENABLED
+/* The shadow stack prevents us from pushing the saved return PC onto
+ the stack and returning normally. Instead we pop the shadow stack
+ and return directly. This is the safest way to return and ensures
+ any stack manipulations done by the vfork'd child doesn't cause the
+ parent to terminate when CET is enabled. */
+# undef SYSCALL_ERROR_HANDLER
+# ifdef PIC
+# define SYSCALL_ERROR_HANDLER \
+0: \
+ calll .L1; \
+.L1: \
+ popl %edx; \
+.L2: \
+ addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx; \
+ movl __libc_errno@gotntpoff(%edx), %edx; \
+ negl %eax; \
+ movl %eax, %gs:(%edx); \
+ orl $-1, %eax; \
+ jmp 1b;
+# else
+# define SYSCALL_ERROR_HANDLER \
+0: \
+ movl __libc_errno@indntpoff, %edx; \
+ negl %eax; \
+ movl %eax, %gs:(%edx); \
+ orl $-1, %eax; \
+ jmp 1b;
+# endif
+# undef SYSCALL_ERROR_LABEL
+# define SYSCALL_ERROR_LABEL 0f
+#endif
/* Clone the calling process, but without copying the whole address space.
The calling process is suspended until the new process exits or is
@@ -38,16 +70,41 @@ ENTRY (__vfork)
movl $SYS_ify (vfork), %eax
int $0x80
+#if !SHSTK_ENABLED
/* Jump to the return PC. Don't jump directly since this
disturbs the branch target cache. Instead push the return
address back on the stack. */
pushl %ecx
cfi_adjust_cfa_offset (4)
+#endif
cmpl $-4095, %eax
/* Branch forward if it failed. */
jae SYSCALL_ERROR_LABEL
+#if SHSTK_ENABLED
+1:
+ /* Check if shadow stack is in use. */
+ xorl %edx, %edx
+ rdsspd %edx
+ testl %edx, %edx
+ /* Normal return if shadow stack isn't in use. */
+ je L(no_shstk)
+
+ /* Pop return address from shadow stack and jump back to caller
+ directly. */
+ movl $1, %edx
+ incsspd %edx
+ jmp *%ecx
+
+L(no_shstk):
+ /* Jump to the return PC. Don't jump directly since this
+ disturbs the branch target cache. Instead push the return
+ address back on the stack. */
+ pushl %ecx
+ cfi_adjust_cfa_offset (4)
+#endif
+
ret
PSEUDO_END (__vfork)
diff --git a/sysdeps/unix/sysv/linux/x86_64/vfork.S b/sysdeps/unix/sysv/linux/x86_64/vfork.S
index e4c8269e3d..8f1ca9f836 100644
--- a/sysdeps/unix/sysv/linux/x86_64/vfork.S
+++ b/sysdeps/unix/sysv/linux/x86_64/vfork.S
@@ -20,6 +20,21 @@
#include <bits/errno.h>
#include <tcb-offsets.h>
+#if SHSTK_ENABLED
+/* The shadow stack prevents us from pushing the saved return PC onto
+ the stack and returning normally. Instead we pop the shadow stack
+ and return directly. This is the safest way to return and ensures
+ any stack manipulations done by the vfork'd child doesn't cause the
+ parent to terminate when CET is enabled. */
+# undef SYSCALL_ERROR_HANDLER
+# define SYSCALL_ERROR_HANDLER \
+0: \
+ SYSCALL_SET_ERRNO; \
+ or $-1, %RAX_LP; \
+ jmp 1b;
+# undef SYSCALL_ERROR_LABEL
+# define SYSCALL_ERROR_LABEL 0f
+#endif
/* Clone the calling process, but without copying the whole address space.
The calling process is suspended until the new process exits or is
@@ -38,13 +53,36 @@ ENTRY (__vfork)
movl $SYS_ify (vfork), %eax
syscall
+#if !SHSTK_ENABLED
/* Push back the return PC. */
pushq %rdi
cfi_adjust_cfa_offset(8)
+#endif
cmpl $-4095, %eax
jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */
+#if SHSTK_ENABLED
+1:
+ /* Check if shadow stack is in use. */
+ xorl %esi, %esi
+ rdsspq %rsi
+ testq %rsi, %rsi
+ /* Normal return if shadow stack isn't in use. */
+ je L(no_shstk)
+
+ /* Pop return address from shadow stack and jump back to caller
+ directly. */
+ movl $1, %esi
+ incsspq %rsi
+ jmp *%rdi
+
+L(no_shstk):
+ /* Push back the return PC. */
+ pushq %rdi
+ cfi_adjust_cfa_offset(8)
+#endif
+
/* Normal return. */
ret
--
2.17.1