[PATCH -v5 03/17] x86/alternatives,jump_label: Provide better text_poke() batching interface

Peter Zijlstra
2019-11-11T14:47:22Z

Adding another text_poke_bp_batch() user made me realize the interface
is all sorts of wrong. The text poke vector should be internal to the
implementation.

This then results in a trivial interface:

text_poke_queue() - which has the 'normal' text_poke_bp() interface
text_poke_finish() - which takes no arguments and flushes any
pending text_poke()s.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/include/asm/text-patching.h | 15 +----
arch/x86/kernel/alternative.c | 64 ++++++++++++++++++++--
arch/x86/kernel/jump_label.c | 99 ++++++++++++-----------------------
3 files changed, 96 insertions(+), 82 deletions(-)

--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -25,14 +25,6 @@ static inline void apply_paravirt(struct
*/
#define POKE_MAX_OPCODE_SIZE 5

-struct text_poke_loc {
- void *addr;
- int len;
- s32 rel32;
- u8 opcode;
- const u8 text[POKE_MAX_OPCODE_SIZE];
-};
-
extern void text_poke_early(void *addr, const void *opcode, size_t len);

/*
@@ -53,9 +45,10 @@ extern void *text_poke(void *addr, const
extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
extern int poke_int3_handler(struct pt_regs *regs);
extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate);
-extern void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries);
-extern void text_poke_loc_init(struct text_poke_loc *tp, void *addr,
- const void *opcode, size_t len, const void *emulate);
+
+extern void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate);
+extern void text_poke_finish(void);
+
extern int after_bootmem;
extern __ro_after_init struct mm_struct *poking_mm;
extern __ro_after_init unsigned long poking_addr;
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -936,6 +936,14 @@ static void do_sync_core(void *info)
sync_core();
}

+struct text_poke_loc {
+ void *addr;
+ int len;
+ s32 rel32;
+ u8 opcode;
+ const u8 text[POKE_MAX_OPCODE_SIZE];
+};
+
static struct bp_patching_desc {
struct text_poke_loc *vec;
int nr_entries;
@@ -1023,6 +1031,10 @@ int poke_int3_handler(struct pt_regs *re
}
NOKPROBE_SYMBOL(poke_int3_handler);

+#define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
+static struct text_poke_loc tp_vec[TP_VEC_MAX];
+static int tp_vec_nr;
+
/**
* text_poke_bp_batch() -- update instructions on live kernel on SMP
* @tp: vector of instructions to patch
@@ -1044,7 +1056,7 @@ NOKPROBE_SYMBOL(poke_int3_handler);
* replacing opcode
* - sync cores
*/
-void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
+static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
{
unsigned char int3 = INT3_INSN_OPCODE;
unsigned int i;
@@ -1118,11 +1130,7 @@ void text_poke_loc_init(struct text_poke
{
struct insn insn;

- if (!opcode)
- opcode = (void *)tp->text;
- else
- memcpy((void *)tp->text, opcode, len);
-
+ memcpy((void *)tp->text, opcode, len);
if (!emulate)
emulate = opcode;

@@ -1167,6 +1175,50 @@ void text_poke_loc_init(struct text_poke
}
}

+/*
+ * We hard rely on the tp_vec being ordered; ensure this is so by flushing
+ * early if needed.
+ */
+static bool tp_order_fail(void *addr)
+{
+ struct text_poke_loc *tp;
+
+ if (!tp_vec_nr)
+ return false;
+
+ if (!addr) /* force */
+ return true;
+
+ tp = &tp_vec[tp_vec_nr - 1];
+ if ((unsigned long)tp->addr > (unsigned long)addr)
+ return true;
+
+ return false;
+}
+
+static void text_poke_flush(void *addr)
+{
+ if (tp_vec_nr == TP_VEC_MAX || tp_order_fail(addr)) {
+ text_poke_bp_batch(tp_vec, tp_vec_nr);
+ tp_vec_nr = 0;
+ }
+}
+
+void text_poke_finish(void)
+{
+ text_poke_flush(NULL);
+}
+
+void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate)
+{
+ struct text_poke_loc *tp;
+
+ text_poke_flush(addr);
+
+ tp = &tp_vec[tp_vec_nr++];
+ text_poke_loc_init(tp, addr, opcode, len, emulate);
+}
+
/**
* text_poke_bp() -- update instructions on live kernel on SMP
* @addr: address to patch
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -35,18 +35,19 @@ static void bug_at(unsigned char *ip, in
BUG();
}

-static void __jump_label_set_jump_code(struct jump_entry *entry,
- enum jump_label_type type,
- union jump_code_union *code,
- int init)
+static const void *
+__jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type, int init)
{
+ static union jump_code_union code; /* relies on text_mutex */
const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
const void *expect;
int line;

- code->jump = 0xe9;
- code->offset = jump_entry_target(entry) -
+ lockdep_assert_held(&text_mutex);
+
+ code.jump = JMP32_INSN_OPCODE;
+ code.offset = jump_entry_target(entry) -
(jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);

if (init) {
@@ -54,23 +55,23 @@ static void __jump_label_set_jump_code(s
} else if (type == JUMP_LABEL_JMP) {
expect = ideal_nop; line = __LINE__;
} else {
- expect = code->code; line = __LINE__;
+ expect = code.code; line = __LINE__;
}

if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
bug_at((void *)jump_entry_code(entry), line);

if (type == JUMP_LABEL_NOP)
- memcpy(code, ideal_nop, JUMP_LABEL_NOP_SIZE);
+ memcpy(&code, ideal_nop, JUMP_LABEL_NOP_SIZE);
+
+ return &code;
}

-static void __ref __jump_label_transform(struct jump_entry *entry,
- enum jump_label_type type,
- int init)
+static void inline __jump_label_transform(struct jump_entry *entry,
+ enum jump_label_type type,
+ int init)
{
- union jump_code_union code;
-
- __jump_label_set_jump_code(entry, type, &code, init);
+ const void *opcode = __jump_label_set_jump_code(entry, type, init);

/*
* As long as only a single processor is running and the code is still
@@ -84,31 +85,33 @@ static void __ref __jump_label_transform
* always nop being the 'currently valid' instruction
*/
if (init || system_state == SYSTEM_BOOTING) {
- text_poke_early((void *)jump_entry_code(entry), &code,
+ text_poke_early((void *)jump_entry_code(entry), opcode,
JUMP_LABEL_NOP_SIZE);
return;
}

- text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE, NULL);
+ text_poke_bp((void *)jump_entry_code(entry), opcode, JUMP_LABEL_NOP_SIZE, NULL);
}

-void arch_jump_label_transform(struct jump_entry *entry,
- enum jump_label_type type)
+static void __ref jump_label_transform(struct jump_entry *entry,
+ enum jump_label_type type,
+ int init)
{
mutex_lock(&text_mutex);
- __jump_label_transform(entry, type, 0);
+ __jump_label_transform(entry, type, init);
mutex_unlock(&text_mutex);
}

-#define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
-static struct text_poke_loc tp_vec[TP_VEC_MAX];
-static int tp_vec_nr;
+void arch_jump_label_transform(struct jump_entry *entry,
+ enum jump_label_type type)
+{
+ jump_label_transform(entry, type, 0);
+}

bool arch_jump_label_transform_queue(struct jump_entry *entry,
enum jump_label_type type)
{
- struct text_poke_loc *tp;
- void *entry_code;
+ const void *opcode;

if (system_state == SYSTEM_BOOTING) {
/*
@@ -118,53 +121,19 @@ bool arch_jump_label_transform_queue(str
return true;
}

- /*
- * No more space in the vector, tell upper layer to apply
- * the queue before continuing.
- */
- if (tp_vec_nr == TP_VEC_MAX)
- return false;
-
- tp = &tp_vec[tp_vec_nr];
-
- entry_code = (void *)jump_entry_code(entry);
-
- /*
- * The INT3 handler will do a bsearch in the queue, so we need entries
- * to be sorted. We can survive an unsorted list by rejecting the entry,
- * forcing the generic jump_label code to apply the queue. Warning once,
- * to raise the attention to the case of an unsorted entry that is
- * better not happen, because, in the worst case we will perform in the
- * same way as we do without batching - with some more overhead.
- */
- if (tp_vec_nr > 0) {
- int prev = tp_vec_nr - 1;
- struct text_poke_loc *prev_tp = &tp_vec[prev];
-
- if (WARN_ON_ONCE(prev_tp->addr > entry_code))
- return false;
- }
-
- __jump_label_set_jump_code(entry, type,
- (union jump_code_union *)&tp->text, 0);
-
- text_poke_loc_init(tp, entry_code, NULL, JUMP_LABEL_NOP_SIZE, NULL);
-
- tp_vec_nr++;
-
+ mutex_lock(&text_mutex);
+ opcode = __jump_label_set_jump_code(entry, type, 0);
+ text_poke_queue((void *)jump_entry_code(entry),
+ opcode, JUMP_LABEL_NOP_SIZE, NULL);
+ mutex_unlock(&text_mutex);
return true;
}

void arch_jump_label_transform_apply(void)
{
- if (!tp_vec_nr)
- return;
-
mutex_lock(&text_mutex);
- text_poke_bp_batch(tp_vec, tp_vec_nr);
+ text_poke_finish();
mutex_unlock(&text_mutex);
-
- tp_vec_nr = 0;
}

static enum {
@@ -193,5 +162,5 @@ __init_or_module void arch_jump_label_tr
jlstate = JL_STATE_NO_UPDATE;
}
if (jlstate == JL_STATE_UPDATE)
- __jump_label_transform(entry, type, 1);
+ jump_label_transform(entry, type, 1);
}