Messages in this thread Patch in this message | | | Date | Sun, 20 Apr 2008 15:44:40 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] Check for breakpoint in text_poke to eliminate bug_on |
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Can you test this new version ? The check was buggy when it fell on a code boundary : the addr - 1 wan't always a valid address.
Check for breakpoint in text_poke to eliminate bug_on
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 | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
Index: linux-2.6-lttng/arch/x86/kernel/alternative.c =================================================================== --- linux-2.6-lttng.orig/arch/x86/kernel/alternative.c 2008-04-20 15:40:30.000000000 -0400 +++ linux-2.6-lttng/arch/x86/kernel/alternative.c 2008-04-20 15:42:08.000000000 -0400 @@ -15,6 +15,7 @@ #include <asm/cacheflush.h> #define MAX_PATCH_LEN (255-1) +#define BREAKPOINT_INSTRUCTION 0xcc #ifdef CONFIG_HOTPLUG_CPU static int smp_alt_once; @@ -505,6 +506,11 @@ 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) { @@ -512,11 +518,9 @@ void *__kprobes text_poke(void *addr, co 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 (is_vmalloc_addr(addr)) { + if (!core_kernel_text((unsigned long)addr)) { pages[0] = vmalloc_to_page(addr); pages[1] = vmalloc_to_page(addr + PAGE_SIZE); } else { @@ -535,5 +539,7 @@ void *__kprobes text_poke(void *addr, co 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
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