[PATCH -v5 10/17] x86/alternative: Shrink text_poke_loc

Peter Zijlstra
2019-11-11T14:48:11Z

Employ the fact that all text must be within a s32 displacement of one
another to shrink the text_poke_loc::addr field. Make it relative to
_stext.

This then shrinks struct text_poke_loc to 16 bytes, and consequently
increases TP_VEC_MAX from 170 to 256.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/alternative.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)

--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -937,7 +937,7 @@ static void do_sync_core(void *info)
}

struct text_poke_loc {
- void *addr;
+ s32 rel_addr; /* addr := _stext + rel_addr */
s32 rel32;
u8 opcode;
const u8 text[POKE_MAX_OPCODE_SIZE];
@@ -948,13 +948,18 @@ static struct bp_patching_desc {
int nr_entries;
} bp_patching;

+static inline void *text_poke_addr(struct text_poke_loc *tp)
+{
+ return _stext + tp->rel_addr;
+}
+
static int notrace patch_cmp(const void *key, const void *elt)
{
struct text_poke_loc *tp = (struct text_poke_loc *) elt;

- if (key < tp->addr)
+ if (key < text_poke_addr(tp))
return -1;
- if (key > tp->addr)
+ if (key > text_poke_addr(tp))
return 1;
return 0;
}
@@ -1000,7 +1005,7 @@ int notrace poke_int3_handler(struct pt_
return 0;
} else {
tp = bp_patching.vec;
- if (tp->addr != ip)
+ if (text_poke_addr(tp) != ip)
return 0;
}

@@ -1078,7 +1083,7 @@ static void text_poke_bp_batch(struct te
* First step: add a int3 trap to the address that will be patched.
*/
for (i = 0; i < nr_entries; i++)
- text_poke(tp[i].addr, &int3, sizeof(int3));
+ text_poke(text_poke_addr(&tp[i]), &int3, sizeof(int3));

on_each_cpu(do_sync_core, NULL, 1);

@@ -1089,7 +1094,7 @@ static void text_poke_bp_batch(struct te
int len = text_opcode_size(tp[i].opcode);

if (len - sizeof(int3) > 0) {
- text_poke((char *)tp[i].addr + sizeof(int3),
+ text_poke(text_poke_addr(&tp[i]) + sizeof(int3),
(const char *)tp[i].text + sizeof(int3),
len - sizeof(int3));
do_sync++;
@@ -1113,7 +1118,7 @@ static void text_poke_bp_batch(struct te
if (tp[i].text[0] == INT3_INSN_OPCODE)
continue;

- text_poke(tp[i].addr, tp[i].text, sizeof(int3));
+ text_poke(text_poke_addr(&tp[i]), tp[i].text, sizeof(int3));
do_sync++;
}

@@ -1143,7 +1148,7 @@ void text_poke_loc_init(struct text_poke
BUG_ON(!insn_complete(&insn));
BUG_ON(len != insn.length);

- tp->addr = addr;
+ tp->rel_addr = addr - (void *)_stext;
tp->opcode = insn.opcode.bytes[0];

switch (tp->opcode) {
@@ -1192,7 +1197,7 @@ static bool tp_order_fail(void *addr)
return true;

tp = &tp_vec[tp_vec_nr - 1];
- if ((unsigned long)tp->addr > (unsigned long)addr)
+ if ((unsigned long)text_poke_addr(tp) > (unsigned long)addr)
return true;

return false;