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Subject[tip:x86/urgent] x86: Don't leak 64-bit kernel register values to 32-bit processes
Commit-ID:  24e35800cdc4350fc34e2bed37b608a9e13ab3b6
Gitweb: http://git.kernel.org/tip/24e35800cdc4350fc34e2bed37b608a9e13ab3b6
Author: Jan Beulich <JBeulich@novell.com>
AuthorDate: Wed, 30 Sep 2009 11:22:11 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 1 Oct 2009 11:24:26 +0200

x86: Don't leak 64-bit kernel register values to 32-bit processes

While 32-bit processes can't directly access R8...R15, they can
gain access to these registers by temporarily switching themselves
into 64-bit mode.

Therefore, registers not preserved anyway by called C functions
(i.e. R8...R11) must be cleared prior to returning to user mode.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: <stable@kernel.org>
LKML-Reference: <4AC34D73020000780001744A@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
arch/x86/ia32/ia32entry.S | 36 +++++++++++++++++++++++-------------
1 files changed, 23 insertions(+), 13 deletions(-)
diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 74619c4..1733f9f 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -21,8 +21,8 @@
#define __AUDIT_ARCH_LE 0x40000000

#ifndef CONFIG_AUDITSYSCALL
-#define sysexit_audit int_ret_from_sys_call
-#define sysretl_audit int_ret_from_sys_call
+#define sysexit_audit ia32_ret_from_sys_call
+#define sysretl_audit ia32_ret_from_sys_call
#endif

#define IA32_NR_syscalls ((ia32_syscall_end - ia32_sys_call_table)/8)
@@ -39,12 +39,12 @@
.endm

/* clobbers %eax */
- .macro CLEAR_RREGS _r9=rax
+ .macro CLEAR_RREGS offset=0, _r9=rax
xorl %eax,%eax
- movq %rax,R11(%rsp)
- movq %rax,R10(%rsp)
- movq %\_r9,R9(%rsp)
- movq %rax,R8(%rsp)
+ movq %rax,\offset+R11(%rsp)
+ movq %rax,\offset+R10(%rsp)
+ movq %\_r9,\offset+R9(%rsp)
+ movq %rax,\offset+R8(%rsp)
.endm

/*
@@ -172,6 +172,10 @@ sysexit_from_sys_call:
movl RIP-R11(%rsp),%edx /* User %eip */
CFI_REGISTER rip,rdx
RESTORE_ARGS 1,24,1,1,1,1
+ xorq %r8,%r8
+ xorq %r9,%r9
+ xorq %r10,%r10
+ xorq %r11,%r11
popfq
CFI_ADJUST_CFA_OFFSET -8
/*CFI_RESTORE rflags*/
@@ -202,7 +206,7 @@ sysexit_from_sys_call:

.macro auditsys_exit exit,ebpsave=RBP
testl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),TI_flags(%r10)
- jnz int_ret_from_sys_call
+ jnz ia32_ret_from_sys_call
TRACE_IRQS_ON
sti
movl %eax,%esi /* second arg, syscall return value */
@@ -218,8 +222,9 @@ sysexit_from_sys_call:
cli
TRACE_IRQS_OFF
testl %edi,TI_flags(%r10)
- jnz int_with_check
- jmp \exit
+ jz \exit
+ CLEAR_RREGS -ARGOFFSET
+ jmp int_with_check
.endm

sysenter_auditsys:
@@ -329,6 +334,9 @@ sysretl_from_sys_call:
CFI_REGISTER rip,rcx
movl EFLAGS-ARGOFFSET(%rsp),%r11d
/*CFI_REGISTER rflags,r11*/
+ xorq %r10,%r10
+ xorq %r9,%r9
+ xorq %r8,%r8
TRACE_IRQS_ON
movl RSP-ARGOFFSET(%rsp),%esp
CFI_RESTORE rsp
@@ -353,7 +361,7 @@ cstar_tracesys:
#endif
xchgl %r9d,%ebp
SAVE_REST
- CLEAR_RREGS r9
+ CLEAR_RREGS 0, r9
movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
movq %rsp,%rdi /* &pt_regs -> arg1 */
call syscall_trace_enter
@@ -425,6 +433,8 @@ ia32_do_call:
call *ia32_sys_call_table(,%rax,8) # xxx: rip relative
ia32_sysret:
movq %rax,RAX-ARGOFFSET(%rsp)
+ia32_ret_from_sys_call:
+ CLEAR_RREGS -ARGOFFSET
jmp int_ret_from_sys_call

ia32_tracesys:
@@ -442,8 +452,8 @@ END(ia32_syscall)

ia32_badsys:
movq $0,ORIG_RAX-ARGOFFSET(%rsp)
- movq $-ENOSYS,RAX-ARGOFFSET(%rsp)
- jmp int_ret_from_sys_call
+ movq $-ENOSYS,%rax
+ jmp ia32_sysret

quiet_ni_syscall:
movq $-ENOSYS,%rax

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