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Commit 6271cfdf authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/mm: Improve stack-overflow #PF handling 



If we get a page fault indicating kernel stack overflow, invoke
handle_stack_overflow().  To prevent us from overflowing the stack
again while handling the overflow (because we are likely to have
very little stack space left), call handle_stack_overflow() on the
double-fault stack.

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/6d6cf96b3fb9b4c9aa303817e1dc4de0c7c36487.1472603235.git.luto@kernel.org


[ Minor edit. ]
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 2b3061c7

arch/x86/include/asm/traps.h

+6 −0
Original line number Diff line number Diff line
@@ -117,6 +117,12 @@ extern void ist_exit(struct pt_regs *regs); 
extern void ist_begin_non_atomic(struct pt_regs *regs);

extern void ist_end_non_atomic(void);



#ifdef CONFIG_VMAP_STACK

void __noreturn handle_stack_overflow(const char *message,

				      struct pt_regs *regs,

				      unsigned long fault_address);

#endif



/* Interrupts/Exceptions */

enum {

	X86_TRAP_DE = 0,	/*  0, Divide-by-zero */

arch/x86/kernel/traps.c

+3 −3
Original line number Diff line number Diff line
@@ -293,7 +293,7 @@ DO_ERROR(X86_TRAP_SS, SIGBUS, "stack segment", stack_segment) 
DO_ERROR(X86_TRAP_AC,     SIGBUS,  "alignment check",		alignment_check)



#ifdef CONFIG_VMAP_STACK

static void __noreturn handle_stack_overflow(const char *message,

__visible void __noreturn handle_stack_overflow(const char *message,

						struct pt_regs *regs,

						unsigned long fault_address)

{

arch/x86/mm/fault.c

+32 −0
Original line number Diff line number Diff line
@@ -753,6 +753,38 @@ no_context(struct pt_regs *regs, unsigned long error_code, 
		return;

	}



#ifdef CONFIG_VMAP_STACK

	/*

	 * Stack overflow?  During boot, we can fault near the initial

	 * stack in the direct map, but that's not an overflow -- check

	 * that we're in vmalloc space to avoid this.

	 */

	if (is_vmalloc_addr((void *)address) &&

	    (((unsigned long)tsk->stack - 1 - address < PAGE_SIZE) ||

	     address - ((unsigned long)tsk->stack + THREAD_SIZE) < PAGE_SIZE)) {

		register void *__sp asm("rsp");

		unsigned long stack = this_cpu_read(orig_ist.ist[DOUBLEFAULT_STACK]) - sizeof(void *);

		/*

		 * We're likely to be running with very little stack space

		 * left.  It's plausible that we'd hit this condition but

		 * double-fault even before we get this far, in which case

		 * we're fine: the double-fault handler will deal with it.

		 *

		 * We don't want to make it all the way into the oops code

		 * and then double-fault, though, because we're likely to

		 * break the console driver and lose most of the stack dump.

		 */

		asm volatile ("movq %[stack], %%rsp\n\t"

			      "call handle_stack_overflow\n\t"

			      "1: jmp 1b"

			      : "+r" (__sp)

			      : "D" ("kernel stack overflow (page fault)"),

				"S" (regs), "d" (address),

				[stack] "rm" (stack));

		unreachable();

	}

#endif



	/*

	 * 32-bit:

	 *