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>

1 files changed, 23 insertions, 13 deletions

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 74619c4f9fda..1733f9f65e82 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