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x86/dumpstack: Improve opcodes dumping in the code section

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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
This commit is contained in:
Borislav Petkov 2018-04-17 18:11:19 +02:00 committed by Thomas Gleixner
parent f0a1d7c11c
commit 9e4a90fd34
1 changed files with 15 additions and 16 deletions
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31
arch/x86/kernel/dumpstack.c
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@ -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;
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 +397,10 @@ 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)
printk(KERN_DEFAULT "Code: Bad RIP value.\n");
else
show_opcodes((u8 *)regs->ip);
}
}