[PATCH v3 41/59] x86/alternatives: Provide text_poke_copy_locked()

Peter Zijlstra
2022-09-15T11:44:32Z

From: Thomas Gleixner <tglx@linutronix.de>

The upcoming call thunk patching must hold text_mutex and needs access to
text_poke_copy(), which takes text_mutex.

Provide a _locked postfixed variant to expose the inner workings.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/include/asm/text-patching.h | 1
arch/x86/kernel/alternative.c | 37 ++++++++++++++++++++---------------
2 files changed, 23 insertions(+), 15 deletions(-)

--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -45,6 +45,7 @@ extern void *text_poke(void *addr, const
extern void text_poke_sync(void);
extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
extern void *text_poke_copy(void *addr, const void *opcode, size_t len);
+extern void *text_poke_copy_locked(void *addr, const void *opcode, size_t len, bool core_ok);
extern void *text_poke_set(void *addr, int c, 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);
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1227,27 +1227,15 @@ void *text_poke_kgdb(void *addr, const v
return __text_poke(text_poke_memcpy, addr, opcode, len);
}

-/**
- * text_poke_copy - Copy instructions into (an unused part of) RX memory
- * @addr: address to modify
- * @opcode: source of the copy
- * @len: length to copy, could be more than 2x PAGE_SIZE
- *
- * Not safe against concurrent execution; useful for JITs to dump
- * new code blocks into unused regions of RX memory. Can be used in
- * conjunction with synchronize_rcu_tasks() to wait for existing
- * execution to quiesce after having made sure no existing functions
- * pointers are live.
- */
-void *text_poke_copy(void *addr, const void *opcode, size_t len)
+void *text_poke_copy_locked(void *addr, const void *opcode, size_t len,
+ bool core_ok)
{
unsigned long start = (unsigned long)addr;
size_t patched = 0;

- if (WARN_ON_ONCE(core_kernel_text(start)))
+ if (WARN_ON_ONCE(!core_ok && core_kernel_text(start)))
return NULL;

- mutex_lock(&text_mutex);
while (patched < len) {
unsigned long ptr = start + patched;
size_t s;
@@ -1257,6 +1245,25 @@ void *text_poke_copy(void *addr, const v
__text_poke(text_poke_memcpy, (void *)ptr, opcode + patched, s);
patched += s;
}
+ return addr;
+}
+
+/**
+ * text_poke_copy - Copy instructions into (an unused part of) RX memory
+ * @addr: address to modify
+ * @opcode: source of the copy
+ * @len: length to copy, could be more than 2x PAGE_SIZE
+ *
+ * Not safe against concurrent execution; useful for JITs to dump
+ * new code blocks into unused regions of RX memory. Can be used in
+ * conjunction with synchronize_rcu_tasks() to wait for existing
+ * execution to quiesce after having made sure no existing functions
+ * pointers are live.
+ */
+void *text_poke_copy(void *addr, const void *opcode, size_t len)
+{
+ mutex_lock(&text_mutex);
+ addr = text_poke_copy_locked(addr, opcode, len, false);
mutex_unlock(&text_mutex);
return addr;
}