Commit 6620ef28 authored by Borislav Petkov's avatar Borislav Petkov
Browse files

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



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: default avatarBorislav Petkov <bp@suse.de>
parent 8e65f6e0

arch/x86/lib/clear_page_64.S

+27 −39
Original line number Diff line number Diff line 
#include <linux/linkage.h>

#include <asm/dwarf2.h>

#include <asm/cpufeature.h>

#include <asm/alternative-asm.h>



/*

 * 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

 * %rdi	- page

 */

ENTRY(clear_page_c)

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)



	/*

	 * 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>

ENDPROC(clear_page_orig)



	.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)

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