This is a note to let you know that I've just added the patch titled
x86_32, entry: Store badsys error code in %eax
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86_32-entry-store-badsys-error-code-in-eax.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8142b215501f8b291a108a202b3a053a265b03dd Mon Sep 17 00:00:00 2001
From: Sven Wegener <sven.wegener@xxxxxxxxxxx>
Date: Tue, 22 Jul 2014 10:26:06 +0200
Subject: x86_32, entry: Store badsys error code in %eax
From: Sven Wegener <sven.wegener@xxxxxxxxxxx>
commit 8142b215501f8b291a108a202b3a053a265b03dd upstream.
Commit 554086d ("x86_32, entry: Do syscall exit work on badsys
(CVE-2014-4508)") introduced a regression in the x86_32 syscall entry
code, resulting in syscall() not returning proper errors for undefined
syscalls on CPUs supporting the sysenter feature.
The following code:
> int result = syscall(666);
> printf("result=%d errno=%d error=%s\n", result, errno, strerror(errno));
results in:
> result=666 errno=0 error=Success
Obviously, the syscall return value is the called syscall number, but it
should have been an ENOSYS error. When run under ptrace it behaves
correctly, which makes it hard to debug in the wild:
> result=-1 errno=38 error=Function not implemented
The %eax register is the return value register. For debugging via ptrace
the syscall entry code stores the complete register context on the
stack. The badsys handlers only store the ENOSYS error code in the
ptrace register set and do not set %eax like a regular syscall handler
would. The old resume_userspace call chain contains code that clobbers
%eax and it restores %eax from the ptrace registers afterwards. The same
goes for the ptrace-enabled call chain. When ptrace is not used, the
syscall return value is the passed-in syscall number from the untouched
%eax register.
Use %eax as the return value register in syscall_badsys and
sysenter_badsys, like a real syscall handler does, and have the caller
push the value onto the stack for ptrace access.
Signed-off-by: Sven Wegener <sven.wegener@xxxxxxxxxxx>
Link: http://lkml.kernel.org/r/alpine.LNX.2.11.1407221022380.31021@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-and-tested-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/entry_32.S | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -428,8 +428,8 @@ sysenter_do_call:
cmpl $(NR_syscalls), %eax
jae sysenter_badsys
call *sys_call_table(,%eax,4)
- movl %eax,PT_EAX(%esp)
sysenter_after_call:
+ movl %eax,PT_EAX(%esp)
LOCKDEP_SYS_EXIT
DISABLE_INTERRUPTS(CLBR_ANY)
TRACE_IRQS_OFF
@@ -510,6 +510,7 @@ ENTRY(system_call)
jae syscall_badsys
syscall_call:
call *sys_call_table(,%eax,4)
+syscall_after_call:
movl %eax,PT_EAX(%esp) # store the return value
syscall_exit:
LOCKDEP_SYS_EXIT
@@ -678,12 +679,12 @@ syscall_fault:
END(syscall_fault)
syscall_badsys:
- movl $-ENOSYS,PT_EAX(%esp)
- jmp syscall_exit
+ movl $-ENOSYS,%eax
+ jmp syscall_after_call
END(syscall_badsys)
sysenter_badsys:
- movl $-ENOSYS,PT_EAX(%esp)
+ movl $-ENOSYS,%eax
jmp sysenter_after_call
END(syscall_badsys)
CFI_ENDPROC
Patches currently in stable-queue which might be from sven.wegener@xxxxxxxxxxx are
queue-3.4/x86_32-entry-store-badsys-error-code-in-eax.patch
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