Introduce a memset like API for text_poke. This will be used to fill the
unused RX memory with illegal instructions.
Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
arch/x86/include/asm/text-patching.h | 1 +
arch/x86/kernel/alternative.c | 67 +++++++++++++++++++++++-----
2 files changed, 58 insertions(+), 10 deletions(-)
diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index d20ab0921480..1cc15528ce29 100644
--- 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 void *opcode, size_t len);
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_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);
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index d374cb3cf024..7563b5bc8328 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -994,7 +994,21 @@ static inline void unuse_temporary_mm(temp_mm_state_t prev_state)
__ro_after_init struct mm_struct *poking_mm;
__ro_after_init unsigned long poking_addr;
-static void *__text_poke(void *addr, const void *opcode, size_t len)
+static void text_poke_memcpy(void *dst, const void *src, size_t len)
+{
+ memcpy(dst, src, len);
+}
+
+static void text_poke_memset(void *dst, const void *src, size_t len)
+{
+ int c = *(const int *)src;
+
+ memset(dst, c, len);
+}
+
+typedef void text_poke_f(void *dst, const void *src, size_t len);
+
+static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t len)
{
bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE;
struct page *pages[2] = {NULL};
@@ -1059,7 +1073,7 @@ static void *__text_poke(void *addr, const void *opcode, size_t len)
prev = use_temporary_mm(poking_mm);
kasan_disable_current();
- memcpy((u8 *)poking_addr + offset_in_page(addr), opcode, len);
+ func((u8 *)poking_addr + offset_in_page(addr), src, len);
kasan_enable_current();
/*
@@ -1087,11 +1101,13 @@ static void *__text_poke(void *addr, const void *opcode, size_t len)
(cross_page_boundary ? 2 : 1) * PAGE_SIZE,
PAGE_SHIFT, false);
- /*
- * If the text does not match what we just wrote then something is
- * fundamentally screwy; there's nothing we can really do about that.
- */
- BUG_ON(memcmp(addr, opcode, len));
+ if (func == text_poke_memcpy) {
+ /*
+ * If the text does not match what we just wrote then something is
+ * fundamentally screwy; there's nothing we can really do about that.
+ */
+ BUG_ON(memcmp(addr, src, len));
+ }
local_irq_restore(flags);
pte_unmap_unlock(ptep, ptl);
@@ -1118,7 +1134,7 @@ void *text_poke(void *addr, const void *opcode, size_t len)
{
lockdep_assert_held(&text_mutex);
- return __text_poke(addr, opcode, len);
+ return __text_poke(text_poke_memcpy, addr, opcode, len);
}
/**
@@ -1137,7 +1153,7 @@ void *text_poke(void *addr, const void *opcode, size_t len)
*/
void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
{
- return __text_poke(addr, opcode, len);
+ return __text_poke(text_poke_memcpy, addr, opcode, len);
}
/**
@@ -1167,7 +1183,38 @@ void *text_poke_copy(void *addr, const void *opcode, size_t len)
s = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(ptr), len - patched);
- __text_poke((void *)ptr, opcode + patched, s);
+ __text_poke(text_poke_memcpy, (void *)ptr, opcode + patched, s);
+ patched += s;
+ }
+ mutex_unlock(&text_mutex);
+ return addr;
+}
+
+/**
+ * text_poke_set - memset into (an unused part of) RX memory
+ * @addr: address to modify
+ * @c: the byte to fill the area with
+ * @len: length to copy, could be more than 2x PAGE_SIZE
+ *
+ * This is useful to overwrite unused regions of RX memory with illegal
+ * instructions.
+ */
+void *text_poke_set(void *addr, int c, size_t len)
+{
+ unsigned long start = (unsigned long)addr;
+ size_t patched = 0;
+
+ if (WARN_ON_ONCE(core_kernel_text(start)))
+ return NULL;
+
+ mutex_lock(&text_mutex);
+ while (patched < len) {
+ unsigned long ptr = start + patched;
+ size_t s;
+
+ s = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(ptr), len - patched);
+
+ __text_poke(text_poke_memset, (void *)ptr, (void *)&c, s);
patched += s;
}
mutex_unlock(&text_mutex);
--
2.30.2
