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x86/lib/clear_page_64.S: Convert to ALTERNATIVE_2 macro

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Move clear_page() up so that we can get 2-byte forward JMPs when
patching:

  apply_alternatives: feat: 3*32+16, old: (ffffffff8130adb0, len: 5), repl: (ffffffff81d0b859, len: 5)
  ffffffff8130adb0: alt_insn: 90 90 90 90 90
  recompute_jump: new_displ: 0x0000003e
  ffffffff81d0b859: rpl_insn: eb 3e 66 66 90

even though the compiler generated 5-byte JMPs which we padded with 5
NOPs.

Also, make the REP_GOOD version be the default as the majority of
machines set REP_GOOD. This way we get to save ourselves the JMP:

  old insn VA: 0xffffffff813038b0, CPU feat: X86_FEATURE_REP_GOOD, size: 5, padlen: 0
  clear_page:

  ffffffff813038b0 <clear_page>:
  ffffffff813038b0:       e9 0b 00 00 00          jmpq ffffffff813038c0
  repl insn: 0xffffffff81cf0e92, size: 0

  old insn VA: 0xffffffff813038b0, CPU feat: X86_FEATURE_ERMS, size: 5, padlen: 0
  clear_page:

  ffffffff813038b0 <clear_page>:
  ffffffff813038b0:       e9 0b 00 00 00          jmpq ffffffff813038c0
  repl insn: 0xffffffff81cf0e92, size: 5
   ffffffff81cf0e92:      e9 69 2a 61 ff          jmpq ffffffff81303900

  ffffffff813038b0 <clear_page>:
  ffffffff813038b0:       e9 69 2a 61 ff          jmpq ffffffff8091631e

Signed-off-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Borislav Petkov 2015-01-18 12:57:41 +01:00
parent 8e65f6e03a
commit 6620ef28c8
1 changed files with 27 additions and 39 deletions
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66
arch/x86/lib/clear_page_64.S
View file

@ -1,31 +1,35 @@
#include <linux/linkage.h>
#include <asm/dwarf2.h>
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>
/*
* Zero a page.
* rdi page
*/
ENTRY(clear_page_c)
* Most CPUs support enhanced REP MOVSB/STOSB instructions. It is
* recommended to use this when possible and we do use them by default.
* If enhanced REP MOVSB/STOSB is not available, try to use fast string.
* Otherwise, use original.
*/
/*
* Zero a page.
* %rdi - page
*/
ENTRY(clear_page)
CFI_STARTPROC
ALTERNATIVE_2 "jmp clear_page_orig", "", X86_FEATURE_REP_GOOD, \
"jmp clear_page_c_e", X86_FEATURE_ERMS
movl $4096/8,%ecx
xorl %eax,%eax
rep stosq
ret
CFI_ENDPROC
ENDPROC(clear_page_c)
ENDPROC(clear_page)
ENTRY(clear_page_c_e)
ENTRY(clear_page_orig)
CFI_STARTPROC
movl $4096,%ecx
xorl %eax,%eax
rep stosb
ret
CFI_ENDPROC
ENDPROC(clear_page_c_e)
ENTRY(clear_page)
CFI_STARTPROC
xorl %eax,%eax
movl $4096/64,%ecx
.p2align 4
@ -45,29 +49,13 @@ ENTRY(clear_page)
nop
ret
CFI_ENDPROC
.Lclear_page_end:
ENDPROC(clear_page)
ENDPROC(clear_page_orig)
/*
* Some CPUs support enhanced REP MOVSB/STOSB instructions.
* It is recommended to use this when possible.
* If enhanced REP MOVSB/STOSB is not available, try to use fast string.
* Otherwise, use original function.
*
*/
#include <asm/cpufeature.h>
.section .altinstr_replacement,"ax"
1: .byte 0xeb /* jmp <disp8> */
.byte (clear_page_c - clear_page) - (2f - 1b) /* offset */
2: .byte 0xeb /* jmp <disp8> */
.byte (clear_page_c_e - clear_page) - (3f - 2b) /* offset */
3:
.previous
.section .altinstructions,"a"
altinstruction_entry clear_page,1b,X86_FEATURE_REP_GOOD,\
.Lclear_page_end-clear_page, 2b-1b, 0
altinstruction_entry clear_page,2b,X86_FEATURE_ERMS, \
.Lclear_page_end-clear_page,3b-2b, 0
.previous
ENTRY(clear_page_c_e)
CFI_STARTPROC
movl $4096,%ecx
xorl %eax,%eax
rep stosb
ret
CFI_ENDPROC
ENDPROC(clear_page_c_e)