lkml.org 
[lkml]   [2003]   [Jan]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] Remove all register pops before sysexit
This patch, which depends on the previous %ebx -> %ebp patch, removes
all pop instruction in the sysenter return path.

This leaks the thread_info address to user mode but this shouldn't be
a security problem.

This is what happens to the various registers:

%eax: return value from system call: already in place
%ebx, %esi, %edi: saved by the C compiler
%ecx, %edx, %ebp: restored by user mode
%esp, eip: copied to %ecx/%edx and restored by sysexit
%ds, %es: initialized to __USER_DS on kernel entry
%cs, %ss: restored by sysexit based on msr
%fs, %gs: not modified by the kernel (saved around context switch)
eflags: not preserved
FP, XMM: any code that modifies them must save/restore them

Note that while it is possible to change %ebx, %esi, %edi, %ecx, %edx
or %ebp via struct pt_regs, anything that does should set TIF_IRET or
another work flag (and it hopefully already does).


diff --exclude-from=/home/ldb/src/exclude -urNdp linux-2.5.54-preldb/arch/i386/kernel/entry.S linux-2.5.54-ldb/arch/i386/kernel/entry.S
--- linux-2.5.54-preldb/arch/i386/kernel/entry.S 2003-01-06 16:01:40.000000000 +0100
+++ linux-2.5.54-ldb/arch/i386/kernel/entry.S 2003-01-06 04:54:58.000000000 +0100
@@ -276,9 +276,9 @@ ENTRY(sysenter_entry)
movl TI_FLAGS(%ebp), %ecx
testw $_TIF_ALLWORK_MASK, %cx
jne syscall_exit_work
- RESTORE_INT_REGS
- movl 12(%esp),%edx
- movl 24(%esp),%ecx
+/* if something modifies registers it must also disable sysexit */
+ movl EIP(%esp), %edx
+ movl OLDESP(%esp), %ecx
sti
sysexit
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2005-03-22 13:32    [W:0.032 / U:0.472 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site