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Subject[PATCH] 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 <osandov@osandov.com>
---
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(+)

diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c
index 778c2f7..a74b53c 100644
--- a/arch/arm/kernel/kgdb.c
+++ b/arch/arm/kernel/kgdb.c
@@ -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
};

--
2.0.3


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