lkml.org 
[lkml]   [2019]   [Oct]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 1/3] x86/alternatives: Teach text_poke_bp() to emulate instructions
On Thu, Oct 03, 2019 at 01:01:06PM +0200, Peter Zijlstra wrote:
> Also, I think text_poke_bp(INT3) is broken, although I don't think
> anybody actually does that. Still, let me fix that.

Something like so should allow text_poke_bp(INT3) to work as expected.

---
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -999,6 +999,13 @@ int poke_int3_handler(struct pt_regs *re
ip += tp->len;

switch (tp->opcode) {
+ case INT3_INSN_OPCODE:
+ /*
+ * Someone poked an explicit INT3, they'll want to handle it,
+ * do not consume.
+ */
+ return 0;
+
case CALL_INSN_OPCODE:
int3_emulate_call(regs, (long)ip + tp->rel32);
break;
@@ -1040,8 +1047,8 @@ NOKPROBE_SYMBOL(poke_int3_handler);
void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
{
unsigned char int3 = INT3_INSN_OPCODE;
- int patched_all_but_first = 0;
unsigned int i;
+ int do_sync;

lockdep_assert_held(&text_mutex);

@@ -1065,16 +1072,16 @@ void text_poke_bp_batch(struct text_poke
/*
* Second step: update all but the first byte of the patched range.
*/
- for (i = 0; i < nr_entries; i++) {
+ for (do_sync = 0, i = 0; i < nr_entries; i++) {
if (tp[i].len - sizeof(int3) > 0) {
text_poke((char *)tp[i].addr + sizeof(int3),
(const char *)tp[i].text + sizeof(int3),
tp[i].len - sizeof(int3));
- patched_all_but_first++;
+ do_sync++;
}
}

- if (patched_all_but_first) {
+ if (do_sync) {
/*
* According to Intel, this core syncing is very likely
* not necessary and we'd be safe even without it. But
@@ -1087,10 +1094,17 @@ void text_poke_bp_batch(struct text_poke
* Third step: replace the first byte (int3) by the first byte of
* replacing opcode.
*/
- for (i = 0; i < nr_entries; i++)
+ for (do_sync = 0, i = 0; i < nr_entries; i++) {
+ if (tp[i].text[0] == INT3_INSN_OPCODE)
+ continue;
+
text_poke(tp[i].addr, tp[i].text, sizeof(int3));
+ do_sync++;
+ }
+
+ if (do_sync)
+ on_each_cpu(do_sync_core, NULL, 1);

- on_each_cpu(do_sync_core, NULL, 1);
/*
* sync_core() implies an smp_mb() and orders this store against
* the writing of the new instruction.
@@ -1123,6 +1137,9 @@ void text_poke_loc_init(struct text_poke
tp->opcode = insn.opcode.bytes[0];

switch (tp->opcode) {
+ case INT3_INSN_OPCPDE:
+ break;
+
case CALL_INSN_OPCODE:
case JMP32_INSN_OPCODE:
case JMP8_INSN_OPCODE:
\
 
 \ /
  Last update: 2019-10-03 14:33    [W:0.142 / U:0.368 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site