Commit 544b4e15 authored by Juergen Gross's avatar Juergen Gross Committed by Borislav Petkov (AMD)
Browse files

x86/alternative: Use helper functions for patching alternatives 



Tidy up apply_alternatives() by moving the main patching action of a single
alternative instance into 3 helper functions:

- analyze_patch_site() for selection whether patching should occur or not and
  to handle nested alternatives.

- prep_patch_site() for applying any needed relocations and issuing debug
  prints for the site.

- patch_site() doing the real patching action, including optimization of any
  padding NOPs.

In prep_patch_site() use __apply_relocation() instead of
text_poke_apply_relocation(), as the NOP optimization is now done in
patch_site() for all cases.

Suggested-by: default avatarBorislav Petkov <bp@alien8.de>
Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20260105080452.5064-2-jgross@suse.com
parent 9ace4753

arch/x86/kernel/alternative.c

+87 −55
Original line number Diff line number Diff line
@@ -586,6 +586,88 @@ static inline u8 * instr_va(struct alt_instr *i) 
	return (u8 *)&i->instr_offset + i->instr_offset;

}



struct patch_site {

	u8 *instr;

	struct alt_instr *alt;

	u8 buff[MAX_PATCH_LEN];

	u8 len;

};



static void __init_or_module analyze_patch_site(struct patch_site *ps,

						struct alt_instr *start,

						struct alt_instr *end)

{

	struct alt_instr *r;



	ps->instr = instr_va(start);

	ps->len = start->instrlen;



	/*

	 * In case of nested ALTERNATIVE()s the outer alternative might add

	 * more padding. To ensure consistent patching find the max padding for

	 * all alt_instr entries for this site (nested alternatives result in

	 * consecutive entries).

	 */

	for (r = start+1; r < end && instr_va(r) == ps->instr; r++) {

		ps->len = max(ps->len, r->instrlen);

		start->instrlen = r->instrlen = ps->len;

	}



	BUG_ON(ps->len > sizeof(ps->buff));

	BUG_ON(start->cpuid >= (NCAPINTS + NBUGINTS) * 32);



	/*

	 * Patch if either:

	 * - feature is present

	 * - feature not present but ALT_FLAG_NOT is set to mean,

	 *   patch if feature is *NOT* present.

	 */

	if (!boot_cpu_has(start->cpuid) == !(start->flags & ALT_FLAG_NOT))

		ps->alt = NULL;

	else

		ps->alt = start;

}



static void __init_or_module prep_patch_site(struct patch_site *ps)

{

	struct alt_instr *alt = ps->alt;

	u8 buff_sz;

	u8 *repl;



	if (!alt) {

		/* Nothing to patch, use original instruction. */

		memcpy(ps->buff, ps->instr, ps->len);

		return;

	}



	repl = (u8 *)&alt->repl_offset + alt->repl_offset;

	DPRINTK(ALT, "feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d) flags: 0x%x",

		alt->cpuid >> 5, alt->cpuid & 0x1f,

		ps->instr, ps->instr, ps->len,

		repl, alt->replacementlen, alt->flags);



	memcpy(ps->buff, repl, alt->replacementlen);

	buff_sz = alt->replacementlen;



	if (alt->flags & ALT_FLAG_DIRECT_CALL)

		buff_sz = alt_replace_call(ps->instr, ps->buff, alt);



	for (; buff_sz < ps->len; buff_sz++)

		ps->buff[buff_sz] = 0x90;



	__apply_relocation(ps->buff, ps->instr, ps->len, repl, alt->replacementlen);



	DUMP_BYTES(ALT, ps->instr, ps->len, "%px:   old_insn: ", ps->instr);

	DUMP_BYTES(ALT, repl, alt->replacementlen, "%px:   rpl_insn: ", repl);

	DUMP_BYTES(ALT, ps->buff, ps->len, "%px: final_insn: ", ps->instr);

}



static void __init_or_module patch_site(struct patch_site *ps)

{

	optimize_nops(ps->instr, ps->buff, ps->len);

	text_poke_early(ps->instr, ps->buff, ps->len);

}



/*

 * Replace instructions with better alternatives for this CPU type. This runs

 * before SMP is initialized to avoid SMP problems with self modifying code.
@@ -599,9 +681,7 @@ static inline u8 * instr_va(struct alt_instr *i) 
void __init_or_module noinline apply_alternatives(struct alt_instr *start,

						  struct alt_instr *end)

{

	u8 insn_buff[MAX_PATCH_LEN];

	u8 *instr, *replacement;

	struct alt_instr *a, *b;

	struct alt_instr *a;



	DPRINTK(ALT, "alt table %px, -> %px", start, end);
@@ -625,59 +705,11 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start, 
	 * order.

	 */

	for (a = start; a < end; a++) {

		unsigned int insn_buff_sz = 0;



		/*

		 * In case of nested ALTERNATIVE()s the outer alternative might

		 * add more padding. To ensure consistent patching find the max

		 * padding for all alt_instr entries for this site (nested

		 * alternatives result in consecutive entries).

		 */

		for (b = a+1; b < end && instr_va(b) == instr_va(a); b++) {

			u8 len = max(a->instrlen, b->instrlen);

			a->instrlen = b->instrlen = len;

		}



		instr = instr_va(a);

		replacement = (u8 *)&a->repl_offset + a->repl_offset;

		BUG_ON(a->instrlen > sizeof(insn_buff));

		BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32);



		/*

		 * Patch if either:

		 * - feature is present

		 * - feature not present but ALT_FLAG_NOT is set to mean,

		 *   patch if feature is *NOT* present.

		 */

		if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {

			memcpy(insn_buff, instr, a->instrlen);

			optimize_nops(instr, insn_buff, a->instrlen);

			text_poke_early(instr, insn_buff, a->instrlen);

			continue;

		}



		DPRINTK(ALT, "feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d) flags: 0x%x",

			a->cpuid >> 5,

			a->cpuid & 0x1f,

			instr, instr, a->instrlen,

			replacement, a->replacementlen, a->flags);



		memcpy(insn_buff, replacement, a->replacementlen);

		insn_buff_sz = a->replacementlen;



		if (a->flags & ALT_FLAG_DIRECT_CALL)

			insn_buff_sz = alt_replace_call(instr, insn_buff, a);



		for (; insn_buff_sz < a->instrlen; insn_buff_sz++)

			insn_buff[insn_buff_sz] = 0x90;



		text_poke_apply_relocation(insn_buff, instr, a->instrlen, replacement, a->replacementlen);



		DUMP_BYTES(ALT, instr, a->instrlen, "%px:   old_insn: ", instr);

		DUMP_BYTES(ALT, replacement, a->replacementlen, "%px:   rpl_insn: ", replacement);

		DUMP_BYTES(ALT, insn_buff, insn_buff_sz, "%px: final_insn: ", instr);

		struct patch_site ps;



		text_poke_early(instr, insn_buff, insn_buff_sz);

		analyze_patch_site(&ps, a, end);

		prep_patch_site(&ps);

		patch_site(&ps);

	}



	kasan_enable_current();