x86/asm/entry/32: Revert 'Do not use R9 in SYSCALL32' commit

This change reverts most of commit 53e9accf0f 'Do not use R9 in
SYSCALL32'. I don't yet understand how, but code in that commit
sometimes fails to preserve EBP.

See https://bugzilla.kernel.org/show_bug.cgi?id=101061
"Problems while executing 32-bit code on AMD64"

Reported-and-tested-by: Krzysztof A. Sobiecki <sobkas@gmail.com>
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Will Drewry <wad@chromium.org>
Cc: Kees Cook <keescook@chromium.org>
CC: x86@kernel.org
Link: http://lkml.kernel.org/r/1437740203-11552-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index bb187a6a877cc62666afb43421eb7e5e8b6fbbfe..5a1844765a7aba6dab47b878daf6eb723c044c03 100644 (file)
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -205,7 +205,6 @@ sysexit_from_sys_call:
        movl    RDX(%rsp), %edx         /* arg3 */
        movl    RSI(%rsp), %ecx         /* arg4 */
        movl    RDI(%rsp), %r8d         /* arg5 */
-       movl    %ebp, %r9d              /* arg6 */
        .endm
 
        .macro auditsys_exit exit
@@ -236,6 +235,7 @@ sysexit_from_sys_call:
 
 sysenter_auditsys:
        auditsys_entry_common
+       movl    %ebp, %r9d              /* reload 6th syscall arg */
        jmp     sysenter_dispatch
 
 sysexit_audit:
@@ -336,7 +336,7 @@ ENTRY(entry_SYSCALL_compat)
         * 32-bit zero extended:
         */
        ASM_STAC
-1:     movl    (%r8), %ebp
+1:     movl    (%r8), %r9d
        _ASM_EXTABLE(1b, ia32_badarg)
        ASM_CLAC
        orl     $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
@@ -346,7 +346,7 @@ ENTRY(entry_SYSCALL_compat)
 cstar_do_call:
        /* 32-bit syscall -> 64-bit C ABI argument conversion */
        movl    %edi, %r8d              /* arg5 */
-       movl    %ebp, %r9d              /* arg6 */
+       /* r9 already loaded */         /* arg6 */
        xchg    %ecx, %esi              /* rsi:arg2, rcx:arg4 */
        movl    %ebx, %edi              /* arg1 */
        movl    %edx, %edx              /* arg3 (zero extension) */
@@ -358,7 +358,6 @@ cstar_dispatch:
        call    *ia32_sys_call_table(, %rax, 8)
        movq    %rax, RAX(%rsp)
 1:
-       movl    RCX(%rsp), %ebp
        DISABLE_INTERRUPTS(CLBR_NONE)
        TRACE_IRQS_OFF
        testl   $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -392,7 +391,9 @@ sysretl_from_sys_call:
 
 #ifdef CONFIG_AUDITSYSCALL
 cstar_auditsys:
+       movl    %r9d, R9(%rsp)          /* register to be clobbered by call */
        auditsys_entry_common
+       movl    R9(%rsp), %r9d          /* reload 6th syscall arg */
        jmp     cstar_dispatch
 
 sysretl_audit:
@@ -404,14 +405,16 @@ cstar_tracesys:
        testl   $(_TIF_WORK_SYSCALL_ENTRY & ~_TIF_SYSCALL_AUDIT), ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
        jz      cstar_auditsys
 #endif
+       xchgl   %r9d, %ebp
        SAVE_EXTRA_REGS
        xorl    %eax, %eax              /* Do not leak kernel information */
        movq    %rax, R11(%rsp)
        movq    %rax, R10(%rsp)
-       movq    %rax, R9(%rsp)
+       movq    %r9, R9(%rsp)
        movq    %rax, R8(%rsp)
        movq    %rsp, %rdi              /* &pt_regs -> arg1 */
        call    syscall_trace_enter
+       movl    R9(%rsp), %r9d
 
        /* Reload arg registers from stack. (see sysenter_tracesys) */
        movl    RCX(%rsp), %ecx
@@ -421,6 +424,7 @@ cstar_tracesys:
        movl    %eax, %eax              /* zero extension */
 
        RESTORE_EXTRA_REGS
+       xchgl   %ebp, %r9d
        jmp     cstar_do_call
 END(entry_SYSCALL_compat)