[tip: x86/alternatives] x86/alternatives: Get rid of __optimize_nops()

tip-bot2 for Borislav Petkov (AMD)
2024-04-09T17:11:33Z

Commit-ID: da8f9cf7e721c690ca169fa88641a6c4cee5cae4
Gitweb: https://git.kernel.org/tip/da8f9cf7e721c690ca169fa88641a6c4cee5cae4
Author: Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate: Tue, 30 Jan 2024 11:59:39 +01:00
Committer: Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 09 Apr 2024 18:12:53 +02:00

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: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-3-bp@alien8.de
---
arch/x86/kernel/alternative.c | 59 +++++++++-------------------------
1 file changed, 16 insertions(+), 43 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index ec94f13..4b3378c 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -217,46 +217,11 @@ static int skip_nops(u8 *buf, int offset, int len)
}

/*
- * 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);