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Commit 9e4a90fd authored by Borislav Petkov's avatar Borislav Petkov Committed by Thomas Gleixner
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x86/dumpstack: Improve opcodes dumping in the code section 



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: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarThomas 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
parent f0a1d7c1

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);

	}

}