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@xxxxxxxxxxxxxxx>
> Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
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
>
