Commit 6bd28856 authored by Will Deacon's avatar Will Deacon Committed by Catalin Marinas
Browse files

arm64: debug: Ensure debug handlers check triggering exception level 



Debug exception handlers may be called for exceptions generated both by
user and kernel code. In many cases, this is checked explicitly, but
in other cases things either happen to work by happy accident or they
go slightly wrong. For example, executing 'brk #4' from userspace will
enter the kprobes code and be ignored, but the instruction will be
retried forever in userspace instead of delivering a SIGTRAP.

Fix this issue in the most stable-friendly fashion by simply adding
explicit checks of the triggering exception level to all of our debug
exception handlers.

Cc: <stable@vger.kernel.org>
Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent b9a4b9d0

arch/arm64/kernel/kgdb.c

+10 −4
Original line number Diff line number Diff line
@@ -244,27 +244,33 @@ int kgdb_arch_handle_exception(int exception_vector, int signo, 


static int kgdb_brk_fn(struct pt_regs *regs, unsigned int esr)

{

	if (user_mode(regs))

		return DBG_HOOK_ERROR;



	kgdb_handle_exception(1, SIGTRAP, 0, regs);

	return 0;

	return DBG_HOOK_HANDLED;

}

NOKPROBE_SYMBOL(kgdb_brk_fn)



static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int esr)

{

	if (user_mode(regs))

		return DBG_HOOK_ERROR;



	compiled_break = 1;

	kgdb_handle_exception(1, SIGTRAP, 0, regs);



	return 0;

	return DBG_HOOK_HANDLED;

}

NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);



static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr)

{

	if (!kgdb_single_step)

	if (user_mode(regs) || !kgdb_single_step)

		return DBG_HOOK_ERROR;



	kgdb_handle_exception(1, SIGTRAP, 0, regs);

	return 0;

	return DBG_HOOK_HANDLED;

}

NOKPROBE_SYMBOL(kgdb_step_brk_fn);

arch/arm64/kernel/probes/kprobes.c

+6 −0
Original line number Diff line number Diff line
@@ -450,6 +450,9 @@ kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr) 
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	int retval;



	if (user_mode(regs))

		return DBG_HOOK_ERROR;



	/* return error if this is not our step */

	retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
@@ -466,6 +469,9 @@ kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr) 
int __kprobes

kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)

{

	if (user_mode(regs))

		return DBG_HOOK_ERROR;



	kprobe_handler(regs);

	return DBG_HOOK_HANDLED;

}

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