ARM: don't enter kgdb when userspace executes a kgdb break instruction.

PATCH In review Omar Sandoval 2 participants 2 messages Aug 1, 2014 Arm (32-bit)

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Omar Sandoval

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2014-08-01 03:05 UTC #0 lore raw

PATCH 1/1 ARM: don't enter kgdb when userspace executes a kgdb break instruction.

The kgdb breakpoint hooks (kgdb_brk_fn and kgdb_compiled_brk_fn) should only be entered when a kgdb break instruction is executed from the kernel. Otherwise, if kgdb is enabled, a userspace program can cause the kernel to drop into the debugger by executing either KGDB_BREAKINST or KGDB_COMPILED_BREAK.

Signed-off-by Omar Sandoval <[email protected]>

---
On a kernel running with kgdb enabled, this program reproduces the problem:
.globl _start
_start:

	udf	#65006	@ KGDB_BREAKINST

The same problem has been fixed in ARM64.

 arch/arm/kernel/kgdb.c | 4 ++++
 1 file changed, 4 insertions(+)

arch/arm/kernel/kgdb.c +4 -0

index 778c2f7..a74b53c 100644
@@ -160,12 +160,16 @@ static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int instr)
 static struct undef_hook kgdb_brkpt_hook = {
 	.instr_mask		= 0xffffffff,
 	.instr_val		= KGDB_BREAKINST,
+	.cpsr_mask		= MODE_MASK,
+	.cpsr_val		= SVC_MODE,
 	.fn			= kgdb_brk_fn
 };
 
 static struct undef_hook kgdb_compiled_brkpt_hook = {
 	.instr_mask		= 0xffffffff,
 	.instr_val		= KGDB_COMPILED_BREAK,
+	.cpsr_mask		= MODE_MASK,
+	.cpsr_val		= SVC_MODE,
 	.fn			= kgdb_compiled_brk_fn
 };

Signature · 1 line

2.0.3

Will Deacon

Acked-by on v1 1/1

2014-08-01 08:10 UTC #1 lore raw

Quoted 27 lines · Omar Sandoval

The kgdb breakpoint hooks (kgdb_brk_fn and kgdb_compiled_brk_fn) should only be entered when a kgdb break instruction is executed from the kernel. Otherwise, if kgdb is enabled, a userspace program can cause the kernel to drop into the debugger by executing either KGDB_BREAKINST or KGDB_COMPILED_BREAK.
Signed-off-by Omar Sandoval <[email protected]>
---
On a kernel running with kgdb enabled, this program reproduces the problem:
.globl _start
_start:
	udf	#65006	@ KGDB_BREAKINST
The same problem has been fixed in ARM64.
 arch/arm/kernel/kgdb.c | 4 ++++
 1 file changed, 4 insertions(+)
arch/arm/kernel/kgdb.c +2 -0
index 778c2f7..a74b53c 100644
@@ -160,12 +160,16 @@ static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int instr)
 static struct undef_hook kgdb_brkpt_hook = {
 	.instr_mask		= 0xffffffff,
 	.instr_val		= KGDB_BREAKINST,
+	.cpsr_mask		= MODE_MASK,
+	.cpsr_val		= SVC_MODE,

arch/arm/kernel/kgdb.c static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int instr) · line 174

Quoted 10 lines

arch/arm/kernel/kgdb.c +2 -0

 	.fn			= kgdb_brk_fn
 };
 
 static struct undef_hook kgdb_compiled_brkpt_hook = {
 	.instr_mask		= 0xffffffff,
 	.instr_val		= KGDB_COMPILED_BREAK,
+	.cpsr_mask		= MODE_MASK,
+	.cpsr_val		= SVC_MODE,
 	.fn			= kgdb_compiled_brk_fn
 };

Acked-by Will Deacon <[email protected]>

Please put this into rmk's patch system.

Cheers,

Will