Commit fe58acef authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

x86/ftrace: Do not jump to direct code in created trampolines 

When creating a trampoline based on the ftrace_regs_caller code, nop out the
jnz test that would jmup to the code that would return to a direct caller
(stored in the ORIG_RAX field) and not back to the function that called it.

Link: http://lkml.kernel.org/r/20200422162750.638839749@goodmis.org



Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 5da7cd11

arch/x86/kernel/ftrace.c

+15 −0
Original line number Diff line number Diff line
@@ -286,6 +286,7 @@ extern void ftrace_regs_caller_ret(void); 
extern void ftrace_caller_end(void);

extern void ftrace_caller_op_ptr(void);

extern void ftrace_regs_caller_op_ptr(void);

extern void ftrace_regs_caller_jmp(void);



/* movq function_trace_op(%rip), %rdx */

/* 0x48 0x8b 0x15 <offset-to-ftrace_trace_op (4 bytes)> */
@@ -316,6 +317,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) 
	unsigned long end_offset;

	unsigned long op_offset;

	unsigned long call_offset;

	unsigned long jmp_offset;

	unsigned long offset;

	unsigned long npages;

	unsigned long size;
@@ -333,11 +335,13 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) 
		end_offset = (unsigned long)ftrace_regs_caller_end;

		op_offset = (unsigned long)ftrace_regs_caller_op_ptr;

		call_offset = (unsigned long)ftrace_regs_call;

		jmp_offset = (unsigned long)ftrace_regs_caller_jmp;

	} else {

		start_offset = (unsigned long)ftrace_caller;

		end_offset = (unsigned long)ftrace_caller_end;

		op_offset = (unsigned long)ftrace_caller_op_ptr;

		call_offset = (unsigned long)ftrace_call;

		jmp_offset = 0;

	}



	size = end_offset - start_offset;
@@ -367,6 +371,17 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) 
	if (WARN_ON(ret < 0))

		goto fail;



	/* No need to test direct calls on created trampolines */

	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {

		/* NOP the jnz 1f; but make sure it's a 2 byte jnz */

		ip = trampoline + (jmp_offset - start_offset);

		if (WARN_ON(*(char *)ip != 0x75))

			goto fail;

		ret = copy_from_kernel_nofault(ip, ideal_nops[2], 2);

		if (ret < 0)

			goto fail;

	}



	/*

	 * The address of the ftrace_ops that is used for this trampoline

	 * is stored at the end of the trampoline. This will be used to

arch/x86/kernel/ftrace_64.S

+1 −0
Original line number Diff line number Diff line
@@ -241,6 +241,7 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL) 
	 */

	movq ORIG_RAX(%rsp), %rax

	testq	%rax, %rax

SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL)

	jnz	1f



	restore_mcount_regs

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