arm64: debug: Ensure debug handlers check triggering exception level

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. For example, executing 'brk #4' from userspace will
enter the kprobes code and be ignored, but the instruction will be
retried forever in userspace instead of delivering a SIGTRAP.

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>
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>

diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index e017a9493b92e907235cc19e7df7e53397c3f56e..72a660a74ff9d7ecc04f113f195e6c8a8d5cf5c1 100644 (file)
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -231,24 +231,33 @@ 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;
 }
 NOKPROBE_SYMBOL(kgdb_brk_fn)
 
 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;
 }
 NOKPROBE_SYMBOL(kgdb_compiled_brk_fn);
 
 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;
 }
 NOKPROBE_SYMBOL(kgdb_step_brk_fn);
 

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index d2b1b624ddc3cf2e41f08c716e278beeb09cf1e0..17f647103ed78106b872e1d33645ffa758e288f5 100644 (file)
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -450,6 +450,9 @@ kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        int retval;
 
+       if (user_mode(regs))
+               return DBG_HOOK_ERROR;
+
        /* return error if this is not our step */
        retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
 
@@ -466,6 +469,9 @@ kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 int __kprobes
 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 {
+       if (user_mode(regs))
+               return DBG_HOOK_ERROR;
+
        kprobe_handler(regs);
        return DBG_HOOK_HANDLED;
 }