On Fri, Mar 01, 2019 at 01:28:00PM +0000, Will Deacon wrote:

FAR_EL1 is UNKNOWN for all debug exceptions other than those caused by taking a hardware watchpoint. Unfortunately, if a debug handler returns a non-zero value, then we will propagate the UNKNOWN FAR value to userspace via the si_addr field of the SIGTRAP siginfo_t.

Instead, let's set si_addr to take on the PC of the faulting instruction, which we have available in the current pt_regs.

Cc: stable@vger.kernel.org Signed-off-by: Will Deacon will.deacon@arm.com

Reviewed-by: Mark Rutland mark.rutland@arm.com

Mark.

---

arch/arm64/mm/fault.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index efb7b2cbead5..ef46925096f0 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -824,11 +824,12 @@ void __init hook_debug_fault_code(int nr, debug_fault_info[nr].name = name; } -asmlinkage int __exception do_debug_exception(unsigned long addr, +asmlinkage int __exception do_debug_exception(unsigned long addr_if_watchpoint, unsigned int esr, struct pt_regs *regs) { const struct fault_info *inf = esr_to_debug_fault_info(esr);

• unsigned long pc = instruction_pointer(regs); int rv;

/* @@ -838,14 +839,14 @@ asmlinkage int __exception do_debug_exception(unsigned long addr, if (interrupts_enabled(regs)) trace_hardirqs_off();

• if (user_mode(regs) && !is_ttbr0_addr(instruction_pointer(regs)))

• if (user_mode(regs) && !is_ttbr0_addr(pc)) arm64_apply_bp_hardening();

• if (!inf->fn(addr, esr, regs)) {

• if (!inf->fn(addr_if_watchpoint, esr, regs)) { rv = 1; } else { arm64_notify_die(inf->name, regs,

• 		 inf->sig, inf->code, (void __user *)addr, esr);
  

• 		 inf->sig, inf->code, (void __user *)pc, esr);
  

  rv = 0; }

2.11.0