It's ok to modify an instruction non-atomically (multiple memory accesses to a
large and/or non aligned instruction) *if and only if* we have inserted a
breakpoint at the beginning of the instruction.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
arch/x86/kernel/alternative.c | 49 ++++++++++++++++++++++++------------------
1 file changed, 29 insertions(+), 20 deletions(-)
Index: linux-2.6-sched-devel/arch/x86/kernel/alternative.c
===================================================================
--- linux-2.6-sched-devel.orig/arch/x86/kernel/alternative.c 2008-04-16 17:17:59.000000000 -0400
+++ linux-2.6-sched-devel/arch/x86/kernel/alternative.c 2008-04-16 17:19:53.000000000 -0400
@@ -15,6 +15,7 @@
#include <asm/io.h>
#define MAX_PATCH_LEN (255-1)
+#define BREAKPOINT_INSTRUCTION 0xcc
#ifdef CONFIG_HOTPLUG_CPU
static int smp_alt_once;
@@ -505,37 +506,45 @@ void *text_poke_early(void *addr, const
* It means the size must be writable atomically and the address must be aligned
* in a way that permits an atomic write. It also makes sure we fit on a single
* page.
+ *
+ * It's ok to modify an instruction non-atomically (multiple memory accesses to
+ * a large and/or non aligned instruction) *if and only if* we have inserted a
+ * breakpoint at the beginning of the instruction and we are modifying the rest
+ * of the instruction.
*/
void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
{
unsigned long flags;
char *vaddr;
int nr_pages = 2;
+ struct page *pages[2];
+ int i;
- BUG_ON(len > sizeof(long));
- BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
- - ((long)addr & ~(sizeof(long) - 1)));
- if (kernel_text_address((unsigned long)addr)) {
- struct page *pages[2] = { virt_to_page(addr),
- virt_to_page(addr + PAGE_SIZE) };
- if (!pages[1])
- nr_pages = 1;
- vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
- BUG_ON(!vaddr);
- local_irq_save(flags);
- memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
- local_irq_restore(flags);
- vunmap(vaddr);
+ if (*((uint8_t *)addr - 1) != BREAKPOINT_INSTRUCTION) {
+ BUG_ON(len > sizeof(long));
+ BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
+ - ((long)addr & ~(sizeof(long) - 1)));
+ }
+ if (!core_kernel_text((unsigned long)addr)) {
+ pages[0] = vmalloc_to_page(addr);
+ pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
} else {
- /*
- * modules are in vmalloc'ed memory, always writable.
- */
- local_irq_save(flags);
- memcpy(addr, opcode, len);
- local_irq_restore(flags);
+ pages[0] = virt_to_page(addr);
+ pages[1] = virt_to_page(addr + PAGE_SIZE);
}
+ BUG_ON(!pages[0]);
+ if (!pages[1])
+ nr_pages = 1;
+ vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
+ BUG_ON(!vaddr);
+ local_irq_save(flags);
+ memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
+ local_irq_restore(flags);
+ vunmap(vaddr);
sync_core();
/* Could also do a CLFLUSH here to speed up CPU recovery; but
that causes hangs on some VIA CPUs. */
+ for (i = 0; i < len; i++)
+ BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
return addr;
}
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
--
