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x86/paravirt: Use relative reference for the original instruction offset

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Similar to the alternative patching, use a relative reference for original
instruction offset rather than absolute one, which saves 8 bytes for one
PARA_SITE entry on x86_64.  As a result, a R_X86_64_PC32 relocation is
generated instead of an R_X86_64_64 one, which also reduces relocation
metadata on relocatable builds. Hardcode the alignment to 4 now.

  [ bp: Massage commit message. ]

Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/9e6053107fbaabc0d33e5d2865c5af2c67ec9925.1686301237.git.houwenlong.hwl@antgroup.com
This commit is contained in:
Hou Wenlong 2023-06-09 17:45:31 +08:00 committed by Borislav Petkov (AMD)
parent b85ea95d08
commit 5c22c4726e
4 changed files with 15 additions and 13 deletions
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10
arch/x86/include/asm/paravirt.h
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@ -743,16 +743,16 @@ void native_pv_lock_init(void) __init;
#else /* __ASSEMBLY__ */
#define _PVSITE(ptype, ops, word, algn) \
#define _PVSITE(ptype, ops) \
771:; \
ops; \
772:; \
.pushsection .parainstructions,"a"; \
.align algn; \
word 771b; \
.align 4; \
.long 771b-.; \
.byte ptype; \
.byte 772b-771b; \
_ASM_ALIGN; \
.align 4; \
.popsection
@ -760,7 +760,7 @@ void native_pv_lock_init(void) __init;
#ifdef CONFIG_PARAVIRT_XXL
#define PARA_PATCH(off) ((off) / 8)
#define PARA_SITE(ptype, ops) _PVSITE(ptype, ops, .quad, 8)
#define PARA_SITE(ptype, ops) _PVSITE(ptype, ops)
#define PARA_INDIRECT(addr) *addr(%rip)
#ifdef CONFIG_DEBUG_ENTRY

8
arch/x86/include/asm/paravirt_types.h
View File

@ -5,7 +5,7 @@
#ifndef __ASSEMBLY__
/* These all sit in the .parainstructions section to tell us what to patch. */
struct paravirt_patch_site {
u8 *instr; /* original instructions */
s32 instr_offset; /* original instructions */
u8 type; /* type of this instruction */
u8 len; /* length of original instruction */
};
@ -263,11 +263,11 @@ extern struct paravirt_patch_template pv_ops;
#define _paravirt_alt(insn_string, type) \
"771:\n\t" insn_string "\n" "772:\n" \
".pushsection .parainstructions,\"a\"\n" \
_ASM_ALIGN "\n" \
_ASM_PTR " 771b\n" \
" .align 4\n" \
" .long 771b-.\n" \
" .byte " type "\n" \
" .byte 772b-771b\n" \
_ASM_ALIGN "\n" \
" .align 4\n" \
".popsection\n"
/* Generate patchable code, with the default asm parameters. */

8
arch/x86/kernel/alternative.c
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@ -1431,20 +1431,22 @@ void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
{
struct paravirt_patch_site *p;
char insn_buff[MAX_PATCH_LEN];
u8 *instr;
for (p = start; p < end; p++) {
unsigned int used;
instr = (u8 *)&p->instr_offset + p->instr_offset;
BUG_ON(p->len > MAX_PATCH_LEN);
/* prep the buffer with the original instructions */
memcpy(insn_buff, p->instr, p->len);
used = paravirt_patch(p->type, insn_buff, (unsigned long)p->instr, p->len);
memcpy(insn_buff, instr, p->len);
used = paravirt_patch(p->type, insn_buff, (unsigned long)instr, p->len);
BUG_ON(used > p->len);
/* Pad the rest with nops */
add_nops(insn_buff + used, p->len - used);
text_poke_early(p->instr, insn_buff, p->len);
text_poke_early(instr, insn_buff, p->len);
}
}
extern struct paravirt_patch_site __start_parainstructions[],

2
arch/x86/kernel/callthunks.c
View File

@ -240,7 +240,7 @@ patch_paravirt_call_sites(struct paravirt_patch_site *start,
struct paravirt_patch_site *p;
for (p = start; p < end; p++)
patch_call(p->instr, ct);
patch_call((void *)&p->instr_offset + p->instr_offset, ct);
}
static __init_or_module void