x86/entry: Reduce the code footprint of the 'idtentry' macro

Play a little trick in the generic PUSH_AND_CLEAR_REGS macro
to insert the GP registers "above" the original return address.

This allows us to (re-)insert the macro in error_entry() and
paranoid_entry() and to remove it from the idtentry macro. This
reduces the static footprint significantly:

   text	   data	    bss	    dec	    hex	filename
  24307	      0	      0	  24307	   5ef3	entry_64.o-orig
  20987	      0	      0	  20987	   51fb	entry_64.o

Co-developed-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180214175924.23065-2-linux@dominikbrodowski.net
[ Small tweaks to comments. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index dce7092..196b610 100644 (file)
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -97,7 +97,7 @@ For 32-bit we have the following conventions - kernel is built with
 
 #define SIZEOF_PTREGS  21*8
 
-.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax
+.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0
        /*
         * Push registers and sanitize registers of values that a
         * speculation attack might otherwise want to exploit. The
@@ -105,8 +105,14 @@ For 32-bit we have the following conventions - kernel is built with
         * could be put to use in a speculative execution gadget.
         * Interleave XOR with PUSH for better uop scheduling:
         */
+       .if \save_ret
+       pushq   %rsi            /* pt_regs->si */
+       movq    8(%rsp), %rsi   /* temporarily store the return address in %rsi */
+       movq    %rdi, 8(%rsp)   /* pt_regs->di (overwriting original return address) */
+       .else
        pushq   %rdi            /* pt_regs->di */
        pushq   %rsi            /* pt_regs->si */
+       .endif
        pushq   \rdx            /* pt_regs->dx */
        pushq   %rcx            /* pt_regs->cx */
        pushq   \rax            /* pt_regs->ax */
@@ -131,6 +137,9 @@ For 32-bit we have the following conventions - kernel is built with
        pushq   %r15            /* pt_regs->r15 */
        xorq    %r15, %r15      /* nospec   r15*/
        UNWIND_HINT_REGS
+       .if \save_ret
+       pushq   %rsi            /* return address on top of stack */
+       .endif
 .endm
 
 .macro POP_REGS pop_rdi=1 skip_r11rcx=0

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 8971bd6..77edc23 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -875,12 +875,8 @@ ENTRY(\sym)
        pushq   $-1                             /* ORIG_RAX: no syscall to restart */
        .endif
 
-       /* Save all registers in pt_regs */
-       PUSH_AND_CLEAR_REGS
-       ENCODE_FRAME_POINTER
-
        .if \paranoid < 2
-       testb   $3, CS(%rsp)                    /* If coming from userspace, switch stacks */
+       testb   $3, CS-ORIG_RAX(%rsp)           /* If coming from userspace, switch stacks */
        jnz     .Lfrom_usermode_switch_stack_\@
        .endif
 
@@ -1130,13 +1126,15 @@ idtentry machine_check          do_mce                  has_error_code=0        paranoid=1
 #endif
 
 /*
- * Switch gs if needed.
+ * Save all registers in pt_regs, and switch gs if needed.
  * Use slow, but surefire "are we in kernel?" check.
  * Return: ebx=0: need swapgs on exit, ebx=1: otherwise
  */
 ENTRY(paranoid_entry)
        UNWIND_HINT_FUNC
        cld
+       PUSH_AND_CLEAR_REGS save_ret=1
+       ENCODE_FRAME_POINTER 8
        movl    $1, %ebx
        movl    $MSR_GS_BASE, %ecx
        rdmsr
@@ -1181,12 +1179,14 @@ ENTRY(paranoid_exit)
 END(paranoid_exit)
 
 /*
- * Switch gs if needed.
+ * Save all registers in pt_regs, and switch GS if needed.
  * Return: EBX=0: came from user mode; EBX=1: otherwise
  */
 ENTRY(error_entry)
-       UNWIND_HINT_REGS offset=8
+       UNWIND_HINT_FUNC
        cld
+       PUSH_AND_CLEAR_REGS save_ret=1
+       ENCODE_FRAME_POINTER 8
        testb   $3, CS+8(%rsp)
        jz      .Lerror_kernelspace
 
@@ -1577,8 +1577,6 @@ end_repeat_nmi:
         * frame to point back to repeat_nmi.
         */
        pushq   $-1                             /* ORIG_RAX: no syscall to restart */
-       PUSH_AND_CLEAR_REGS
-       ENCODE_FRAME_POINTER
 
        /*
         * Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit