Commit da8f9cf7 authored by Borislav Petkov (AMD)'s avatar Borislav Petkov (AMD)
Browse files

x86/alternatives: Get rid of __optimize_nops() 



There's no need to carve out bits of the NOP optimization functionality
and look at JMP opcodes - simply do one more NOPs optimization pass
at the end of patching.

A lot simpler code.

Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-3-bp@alien8.de
parent f796c758

arch/x86/kernel/alternative.c

+16 −43
Original line number Diff line number Diff line
@@ -216,47 +216,12 @@ static int skip_nops(u8 *buf, int offset, int len) 
	return offset;

}



/*

 * Optimize a sequence of NOPs, possibly preceded by an unconditional jump

 * to the end of the NOP sequence into a single NOP.

 */

static bool

__optimize_nops(const u8 * const instr, u8 *buf, size_t len, struct insn *insn, int *next, int *prev, int *target)

{

	int i = *next - insn->length;



	switch (insn->opcode.bytes[0]) {

	case JMP8_INSN_OPCODE:

	case JMP32_INSN_OPCODE:

		*prev = i;

		*target = *next + insn->immediate.value;

		return false;

	}



	if (insn_is_nop(insn)) {

		int nop = i;



		*next = skip_nops(buf, *next, len);

		if (*target && *next == *target)

			nop = *prev;



		add_nop(buf + nop, *next - nop);

		DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);

		return true;

	}



	*target = 0;

	return false;

}



/*

 * "noinline" to cause control flow change and thus invalidate I$ and

 * cause refetch after modification.

 */

static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)

static void noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)

{

	int prev, target = 0;



	for (int next, i = 0; i < len; i = next) {

		struct insn insn;
@@ -265,7 +230,14 @@ static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 * 


		next = i + insn.length;



		__optimize_nops(instr, buf, len, &insn, &next, &prev, &target);

		if (insn_is_nop(&insn)) {

			int nop = i;



			next = skip_nops(buf, next, len);



			add_nop(buf + nop, next - nop);

			DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, next);

		}

	}

}
@@ -339,10 +311,8 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len) 
	return (target < src || target > src + src_len);

}



void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)

static void __apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)

{

	int prev, target = 0;



	for (int next, i = 0; i < instrlen; i = next) {

		struct insn insn;
@@ -351,9 +321,6 @@ void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl 


		next = i + insn.length;



		if (__optimize_nops(instr, buf, instrlen, &insn, &next, &prev, &target))

			continue;



		switch (insn.opcode.bytes[0]) {

		case 0x0f:

			if (insn.opcode.bytes[1] < 0x80 ||
@@ -398,6 +365,12 @@ void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl 
	}

}



void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)

{

	__apply_relocation(buf, instr, instrlen, repl, repl_len);

	optimize_nops(instr, buf, repl_len);

}



/* Low-level backend functions usable from alternative code replacements. */

DEFINE_ASM_FUNC(nop_func, "", .entry.text);

EXPORT_SYMBOL_GPL(nop_func);