[PATCH 4.4 BACKPORT 1/2] arm64: debug: Don't propagate UNKNOWN FAR into si_code for debug signals

[PATCH 4.4 BACKPORT 1/2] arm64: debug: Don't propagate UNKNOWN FAR into si_code for debug signals

[Will Deacon]

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> # 4.4.y
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>
---
 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 04c4b88706d8..89abdf9af4e6 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -589,11 +589,12 @@ 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;
 
@@ -604,16 +605,16 @@ asmlinkage int __exception do_debug_exception(unsigned long addr,
 	if (interrupts_enabled(regs))
 		trace_hardirqs_off();
 
-	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;
 	}
-- 
2.11.0

[PATCH 4.4 BACKPORT 2/2] arm64: debug: Ensure debug handlers check triggering exception level

[Will Deacon]

Commit 6bd288569b50bc89fa5513031086746968f585cb upstream.

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.

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> # 4.4.y
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>
---
 arch/arm64/kernel/kgdb.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index bcac81e600b9..f72743dc070d 100644
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -215,22 +215,31 @@ 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;
 }
 
 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;
 }
 
 static int kgdb_step_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;
 }
 
 static struct break_hook kgdb_brkpt_hook = {
-- 
2.11.0