Commit 1f368393 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)
Browse files

x86/kprobes: Push a fake return address at kretprobe_trampoline 

Change __kretprobe_trampoline() to push the address of the
__kretprobe_trampoline() as a fake return address at the bottom
of the stack frame. This fake return address will be replaced
with the correct return address in the trampoline_handler().

With this change, the ORC unwinder can check whether the return
address is modified by kretprobes or not.

Link: https://lkml.kernel.org/r/163163054185.489837.14338744048957727386.stgit@devnote2



Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Suggested-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Tested-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent df91c5bc

arch/x86/kernel/kprobes/core.c

+25 −9
Original line number Diff line number Diff line
@@ -1022,28 +1022,33 @@ asm( 
	".global __kretprobe_trampoline\n"

	".type __kretprobe_trampoline, @function\n"

	"__kretprobe_trampoline:\n"

	/* We don't bother saving the ss register */

#ifdef CONFIG_X86_64

	"	pushq %rsp\n"

	/* Push a fake return address to tell the unwinder it's a kretprobe. */

	"	pushq $__kretprobe_trampoline\n"

	UNWIND_HINT_FUNC

	/* Save the 'sp - 8', this will be fixed later. */

	"	pushq %rsp\n"

	"	pushfq\n"

	SAVE_REGS_STRING

	"	movq %rsp, %rdi\n"

	"	call trampoline_handler\n"

	/* Replace saved sp with true return address. */

	"	movq %rax, 19*8(%rsp)\n"

	RESTORE_REGS_STRING

	/* In trampoline_handler(), 'regs->flags' is copied to 'regs->sp'. */

	"	addq $8, %rsp\n"

	"	popfq\n"

#else

	"	pushl %esp\n"

	/* Push a fake return address to tell the unwinder it's a kretprobe. */

	"	pushl $__kretprobe_trampoline\n"

	UNWIND_HINT_FUNC

	/* Save the 'sp - 4', this will be fixed later. */

	"	pushl %esp\n"

	"	pushfl\n"

	SAVE_REGS_STRING

	"	movl %esp, %eax\n"

	"	call trampoline_handler\n"

	/* Replace saved sp with true return address. */

	"	movl %eax, 15*4(%esp)\n"

	RESTORE_REGS_STRING

	/* In trampoline_handler(), 'regs->flags' is copied to 'regs->sp'. */

	"	addl $4, %esp\n"

	"	popfl\n"

#endif

	"	ret\n"
@@ -1063,8 +1068,10 @@ STACK_FRAME_NON_STANDARD_FP(__kretprobe_trampoline); 
/*

 * Called from __kretprobe_trampoline

 */

__used __visible void *trampoline_handler(struct pt_regs *regs)

__used __visible void trampoline_handler(struct pt_regs *regs)

{

	unsigned long *frame_pointer;



	/* fixup registers */

	regs->cs = __KERNEL_CS;

#ifdef CONFIG_X86_32
@@ -1072,8 +1079,17 @@ __used __visible void *trampoline_handler(struct pt_regs *regs) 
#endif

	regs->ip = (unsigned long)&__kretprobe_trampoline;

	regs->orig_ax = ~0UL;

	regs->sp += sizeof(long);

	frame_pointer = &regs->sp + 1;



	/* Replace fake return address with real one. */

	*frame_pointer = kretprobe_trampoline_handler(regs, frame_pointer);



	return (void *)kretprobe_trampoline_handler(regs, &regs->sp);

	/*

	 * Copy FLAGS to 'pt_regs::sp' so that __kretprobe_trapmoline()

	 * can do RET right after POPF.

	 */

	regs->sp = regs->flags;

}

NOKPROBE_SYMBOL(trampoline_handler);