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Subject[PATCH 5.0 172/238] arm64: debug: Dont propagate UNKNOWN FAR into si_code for debug signals
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will.deacon@arm.com>

commit b9a4b9d084d978f80eb9210727c81804588b42ff upstream.

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>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- 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_exce
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;
}


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