Messages in this thread Patch in this message | | | Date | Wed, 30 Jul 2014 00:12:45 -0700 | From | Omar Sandoval <> | Subject | [PATCH] ARM/ARM64: don't enter kgdb when userspace executes a kgdb break instruction. |
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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 on ARM, or brk #KGDB_{DYN,COMPILED}_DGB_BRK_IMM on ARM64.
Signed-off-by: Omar Sandoval <osandov@osandov.com> --- The following program reproduces the fixed problem on ARM: .globl _start _start: udf #65006 @ KGDB_BREAKINST
And on ARM64: .globl _start _start: brk #0x400 @ KGDB_DYN_DGB_BRK_IMM
arch/arm/kernel/kgdb.c | 4 ++++ arch/arm64/include/asm/debug-monitors.h | 4 +++- arch/arm64/kernel/debug-monitors.c | 3 ++- arch/arm64/kernel/kgdb.c | 4 ++++ 4 files changed, 13 insertions(+), 2 deletions(-)
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 }; diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h index 6e9b5b3..e1d27ce 100644 --- a/arch/arm64/include/asm/debug-monitors.h +++ b/arch/arm64/include/asm/debug-monitors.h @@ -105,8 +105,10 @@ void unregister_step_hook(struct step_hook *hook); struct break_hook { struct list_head node; - u32 esr_val; u32 esr_mask; + u32 esr_val; + u64 pstate_mask; + u64 pstate_val; int (*fn)(struct pt_regs *regs, unsigned int esr); }; diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index a7fb874..594fac4 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -303,7 +303,8 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr) read_lock(&break_hook_lock); list_for_each_entry(hook, &break_hook, node) - if ((esr & hook->esr_mask) == hook->esr_val) + if ((esr & hook->esr_mask) == hook->esr_val && + (regs->pstate & hook->pstate_mask) == hook->pstate_val) fn = hook->fn; read_unlock(&break_hook_lock); diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c index 75c9cf1..80eb035 100644 --- a/arch/arm64/kernel/kgdb.c +++ b/arch/arm64/kernel/kgdb.c @@ -236,12 +236,16 @@ static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr) static struct break_hook kgdb_brkpt_hook = { .esr_mask = 0xffffffff, .esr_val = DBG_ESR_VAL_BRK(KGDB_DYN_DGB_BRK_IMM), + .pstate_mask = PSR_MODE_MASK, + .pstate_val = PSR_MODE_EL1h, .fn = kgdb_brk_fn }; static struct break_hook kgdb_compiled_brkpt_hook = { .esr_mask = 0xffffffff, .esr_val = DBG_ESR_VAL_BRK(KDBG_COMPILED_DBG_BRK_IMM), + .pstate_mask = PSR_MODE_MASK, + .pstate_val = PSR_MODE_EL1h, .fn = kgdb_compiled_brk_fn }; -- 2.0.3
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