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 --- 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 #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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/