x86/dumpstack: Improve opcodes dumping in the code section (9e4a90fd) · Commits · 戴 / test

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 it's serialized via 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 <bp@suse.de> Signed-off-by:

Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andy Lutomirski <luto@amacapital.net> Link: https://lkml.kernel.org/r/20180417161124.5294-5-bp@alien8.de

arch/x86/kernel/dumpstack.c

+15 −16

Original line number	Diff line number	Diff line
		@@ -72,29 +72,24 @@ 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;
		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;
		}
		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 (probe_kernel_read(opcodes, ip, OPCODE_BUFSIZE)) {
		pr_cont("Bad RIP value.\n");
		return;
		}
		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 +397,10 @@ void show_regs(struct pt_regs *regs)
		*/
		if (!user_mode(regs)) {
		show_trace_log_lvl(current, regs, NULL, KERN_DEFAULT);

		if (regs->ip < PAGE_OFFSET)
		printk(KERN_DEFAULT "Code: Bad RIP value.\n");
		else
		show_opcodes((u8 *)regs->ip);
		}
		}

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