renegade-project/linux-next
2
0
Fork 0
mirror of https://github.com/edk2-porting/linux-next.git synced 2024-12-28 07:04:00 +08:00
Code

x86_32, entry: Store badsys error code in %eax

Browse Source 
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@stealer.net>
Link: http://lkml.kernel.org/r/alpine.LNX.2.11.1407221022380.31021@titan.int.lan.stealer.net
Reviewed-and-tested-by: Andy Lutomirski <luto@amacapital.net>
Cc: <stable@vger.kernel.org> # If 554086d is backported
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Sven Wegener 2014-07-22 10:26:06 +02:00 committed by H. Peter Anvin
parent 9a3c4145af
commit 8142b21550
1 changed files with 5 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
arch/x86/kernel/entry_32.S
View File

@ -425,8 +425,8 @@ 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
@ -502,6 +502,7 @@ 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
@ -675,12 +676,12 @@ 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