x86/asm/entry/64: Get rid of the FIXUP_TOP_OF_STACK/RESTORE_TOP_OF_STACK macros

The FIXUP_TOP_OF_STACK macro is only necessary because we don't save %r11
to pt_regs->r11 on SYSCALL64 fast path, but we want ptrace to see it populated.

Bite the bullet, add a single additional PUSH instruction, and remove
the FIXUP_TOP_OF_STACK macro.

The RESTORE_TOP_OF_STACK macro is already a nop. Remove it too.

On SandyBridge CPU, it does not get slower:
measured 54.22 ns per getpid syscall before and after last two
changes on defconfig kernel.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1426785469-15125-4-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 3ea4f6d..3f8daba 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -22,8 +22,6 @@
  * - CFI macros are used to generate dwarf2 unwind information for better
  * backtraces. They don't change any code.
  * - ENTRY/END Define functions in the symbol table.
- * - FIXUP_TOP_OF_STACK/RESTORE_TOP_OF_STACK - Fix up the hardware stack
- * frame that is otherwise undefined after a SYSCALL
  * - TRACE_IRQ_* - Trace hard interrupt state for lock debugging.
  * - idtentry - Define exception entry points.
  */
@@ -118,23 +116,6 @@ ENDPROC(native_usergs_sysret64)
 # define TRACE_IRQS_IRETQ_DEBUG                TRACE_IRQS_IRETQ
 #endif
 
-/*
- * C code is not supposed to know that the iret frame is not populated.
- * Every time a C function with an pt_regs argument is called from
- * the SYSCALL based fast path FIXUP_TOP_OF_STACK is needed.
- * RESTORE_TOP_OF_STACK syncs the syscall state after any possible ptregs
- * manipulation.
- */
-       .macro FIXUP_TOP_OF_STACK tmp offset=0
-       /* copy flags to r11 as sysret would do */
-       movq EFLAGS+\offset(%rsp),\tmp
-       movq \tmp,R11+\offset(%rsp)
-       .endm
-
-       .macro RESTORE_TOP_OF_STACK tmp offset=0
-       /* nothing to do */
-       .endm
-
 /*
  * empty frame
  */
@@ -265,7 +246,8 @@ GLOBAL(system_call_after_swapgs)
        pushq_cfi_reg   r8                      /* pt_regs->r8 */
        pushq_cfi_reg   r9                      /* pt_regs->r9 */
        pushq_cfi_reg   r10                     /* pt_regs->r10 */
-       sub     $(7*8),%rsp /* pt_regs->r11,bp,bx,r12-15 not saved */
+       pushq_cfi_reg   r11                     /* pt_regs->r11 */
+       sub     $(6*8),%rsp /* pt_regs->bp,bx,r12-15 not saved */
 
        testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,SIZEOF_PTREGS)
        jnz tracesys
@@ -312,7 +294,6 @@ ret_from_sys_call:
        CFI_RESTORE_STATE
 
 int_ret_from_sys_call_fixup:
-       FIXUP_TOP_OF_STACK %r11
        jmp int_ret_from_sys_call
 
        /* Do syscall entry tracing */
@@ -328,7 +309,6 @@ tracesys:
 
 tracesys_phase2:
        SAVE_EXTRA_REGS
-       FIXUP_TOP_OF_STACK %rdi
        movq %rsp, %rdi
        movq $AUDIT_ARCH_X86_64, %rsi
        movq %rax,%rdx
@@ -421,9 +401,7 @@ ENTRY(stub_\func)
        CFI_STARTPROC
        DEFAULT_FRAME 0, 8              /* offset 8: return address */
        SAVE_EXTRA_REGS 8
-       FIXUP_TOP_OF_STACK %r11, 8
        call sys_\func
-       RESTORE_TOP_OF_STACK %r11, 8
        ret
        CFI_ENDPROC
 END(stub_\func)
@@ -438,7 +416,6 @@ ENTRY(stub_execve)
        addq $8, %rsp
        DEFAULT_FRAME 0
        SAVE_EXTRA_REGS
-       FIXUP_TOP_OF_STACK %r11
        call sys_execve
        movq %rax,RAX(%rsp)
        RESTORE_EXTRA_REGS
@@ -451,9 +428,7 @@ ENTRY(stub_execveat)
        addq $8, %rsp
        DEFAULT_FRAME 0
        SAVE_EXTRA_REGS
-       FIXUP_TOP_OF_STACK %r11
        call sys_execveat
-       RESTORE_TOP_OF_STACK %r11
        movq %rax,RAX(%rsp)
        RESTORE_EXTRA_REGS
        jmp int_ret_from_sys_call
@@ -469,7 +444,6 @@ ENTRY(stub_rt_sigreturn)
        addq $8, %rsp
        DEFAULT_FRAME 0
        SAVE_EXTRA_REGS
-       FIXUP_TOP_OF_STACK %r11
        call sys_rt_sigreturn
        movq %rax,RAX(%rsp) # fixme, this could be done at the higher layer
        RESTORE_EXTRA_REGS
@@ -483,7 +457,6 @@ ENTRY(stub_x32_rt_sigreturn)
        addq $8, %rsp
        DEFAULT_FRAME 0
        SAVE_EXTRA_REGS
-       FIXUP_TOP_OF_STACK %r11
        call sys32_x32_rt_sigreturn
        movq %rax,RAX(%rsp) # fixme, this could be done at the higher layer
        RESTORE_EXTRA_REGS
@@ -496,9 +469,7 @@ ENTRY(stub_x32_execve)
        addq $8, %rsp
        DEFAULT_FRAME 0
        SAVE_EXTRA_REGS
-       FIXUP_TOP_OF_STACK %r11
        call compat_sys_execve
-       RESTORE_TOP_OF_STACK %r11
        movq %rax,RAX(%rsp)
        RESTORE_EXTRA_REGS
        jmp int_ret_from_sys_call
@@ -510,9 +481,7 @@ ENTRY(stub_x32_execveat)
        addq $8, %rsp
        DEFAULT_FRAME 0
        SAVE_EXTRA_REGS
-       FIXUP_TOP_OF_STACK %r11
        call compat_sys_execveat
-       RESTORE_TOP_OF_STACK %r11
        movq %rax,RAX(%rsp)
        RESTORE_EXTRA_REGS
        jmp int_ret_from_sys_call