arm64: debug: Don't propagate UNKNOWN FAR into si_code for debug signals

BugLink: https://bugs.launchpad.net/bugs/1838116
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index dd8f5197b549d094b813712da89c11a0fe072864..1be6e6f95c3ad5d6f4c48ce6da3c4555b5039eca 100644 (file)
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -787,11 +787,12 @@ 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 = debug_fault_info + DBG_ESR_EVT(esr);
+       unsigned long pc = instruction_pointer(regs);
        struct siginfo info;
        int rv;
 
@@ -802,19 +803,19 @@ asmlinkage int __exception do_debug_exception(unsigned long addr,
        if (interrupts_enabled(regs))
                trace_hardirqs_off();
 
-       if (user_mode(regs) && instruction_pointer(regs) > TASK_SIZE)
+       if (user_mode(regs) && pc > TASK_SIZE)
                arm64_apply_bp_hardening();
 
-       if (!inf->fn(addr, esr, regs)) {
+       if (!inf->fn(addr_if_watchpoint, esr, regs)) {
                rv = 1;
        } else {
                pr_alert("Unhandled debug exception: %s (0x%08x) at 0x%016lx\n",
-                        inf->name, esr, addr);
+                        inf->name, esr, pc);
 
                info.si_signo = inf->sig;
                info.si_errno = 0;
                info.si_code  = inf->code;
-               info.si_addr  = (void __user *)addr;
+               info.si_addr  = (void __user *)pc;
                arm64_notify_die("", regs, &info, 0);
                rv = 0;
        }