From: Borislav Petkov <[email protected]> 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 <[email protected]> --- 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; } - for (i = 0; i < code_len; i++, ip++) { - if (ip < (u8 *)PAGE_OFFSET || probe_kernel_address(ip, c)) { - pr_cont(" Bad RIP value."); - break; - } - if (ip == (u8 *)rip) - pr_cont("<%02x> ", c); + + for (i = 0; i < OPCODE_BUFSIZE; i++, ip++) { + if (ip == rip) + pr_cont("<%02x> ", opcodes[i]); else - pr_cont("%02x ", c); + pr_cont("%02x ", opcodes[i]); } pr_cont("\n"); } @@ -402,6 +396,10 @@ void show_regs(struct pt_regs *regs) */ if (!user_mode(regs)) { show_trace_log_lvl(current, regs, NULL, KERN_DEFAULT); - show_opcodes((u8 *)regs->ip); + + if (regs->ip < PAGE_OFFSET) + pr_cont(" Bad RIP value.\n"); + else + show_opcodes((u8 *)regs->ip); } } -- 2.13.0
