On Thu, Mar 15, 2018 at 04:44:43PM +0100, Borislav Petkov wrote:
> From: Borislav Petkov <b...@suse.de>
>
> The code used to iterate byte-by-byte over the bytes around RIP and that
> is expensive: disabling pagefaults around it, copy_from_user, etc...
>
> Make it read the whole buffer of OPCODE_BUFSIZE size in one go. Use a
> statically allocated 64 bytes buffer so that concurrent show_opcodes()
> do not interleave in the output even though in the majority of the cases
> we sync on die_lock. Except the #PF path which doesn't...
>
> Also, do the PAGE_OFFSET check outside of the function because latter
> will be reused in other context.
>
> Signed-off-by: Borislav Petkov <b...@suse.de>
> ---
> arch/x86/kernel/dumpstack.c | 34 ++++++++++++++++------------------
> 1 file changed, 16 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index eb9d6c00a52f..3f781a8dddb8 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -22,8 +22,6 @@
> #include <asm/stacktrace.h>
> #include <asm/unwind.h>
>
> -#define OPCODE_BUFSIZE 64
> -
> int panic_on_unrecovered_nmi;
> int panic_on_io_nmi;
> static int die_counter;
> @@ -72,29 +70,25 @@ static void printk_stack_address(unsigned long address,
> int reliable,
>
> static void show_opcodes(u8 *rip)
> {
> - unsigned int code_prologue = OPCODE_BUFSIZE * 43 / 64;
> - unsigned int code_len = OPCODE_BUFSIZE;
> - unsigned char c;
> +#define OPCODE_BUFSIZE 64
> + unsigned int code_prologue = OPCODE_BUFSIZE * 2 / 3;
> + u8 opcodes[OPCODE_BUFSIZE];
> u8 *ip;
> int i;
>
> printk(KERN_DEFAULT "Code: ");
>
> ip = (u8 *)rip - code_prologue;
> - if (ip < (u8 *)PAGE_OFFSET || probe_kernel_address(ip, c)) {
> - /* try starting at IP */
> - ip = (u8 *)rip;
> - code_len = code_len - code_prologue + 1;
> + if (probe_kernel_read(opcodes, ip, OPCODE_BUFSIZE)) {
> + pr_cont(" Bad RIP value.\n");
> + return;
As long as you're changing the code, might as well remove the leading
space here, so it shows
Code: Bad RIP value.
instead of
Code: Bad RIP value.
--
Josh
