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[4.4,002/168] arm64: debug: Ensure debug handlers check triggering exception level

Message ID 20190424170923.593936482@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg KH April 24, 2019, 5:07 p.m. UTC 
From: Will Deacon <will.deacon@arm.com>


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>


---
 arch/arm64/kernel/kgdb.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)
diff mbox series

Patch

--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -215,22 +215,31 @@  int kgdb_arch_handle_exception(int excep
 
 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 = {