diff options
| author |   Will Deacon <will@kernel.org> | 2020-02-13 12:06:26 +0000 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2020-07-16 11:41:21 +0100 |
| commit | 3a5a4366cecc25daa300b9a9174f7fdd352b9068 (patch) | |
| tree | cab8688b96d324ee0b110d0525679eee6f2a43e5 /arch/arm64/kernel/ptrace.c | |
| parent | arm64: ptrace: Consistently use pseudo-singlestep exceptions (diff) | |
| download | linux-dev-3a5a4366cecc25daa300b9a9174f7fdd352b9068.tar.xz linux-dev-3a5a4366cecc25daa300b9a9174f7fdd352b9068.zip | |
arm64: ptrace: Override SPSR.SS when single-stepping is enabled
Luis reports that, when reverse debugging with GDB, single-step does not
function as expected on arm64:
| I've noticed, under very specific conditions, that a PTRACE_SINGLESTEP
| request by GDB won't execute the underlying instruction. As a consequence,
| the PC doesn't move, but we return a SIGTRAP just like we would for a
| regular successful PTRACE_SINGLESTEP request.
The underlying problem is that when the CPU register state is restored
as part of a reverse step, the SPSR.SS bit is cleared and so the hardware
single-step state can transition to the "active-pending" state, causing
an unexpected step exception to be taken immediately if a step operation
is attempted.
In hindsight, we probably shouldn't have exposed SPSR.SS in the pstate
accessible by the GPR regset, but it's a bit late for that now. Instead,
simply prevent userspace from configuring the bit to a value which is
inconsistent with the TIF_SINGLESTEP state for the task being traced.
Cc: <stable@vger.kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Keno Fischer <keno@juliacomputing.com>
Link: https://lore.kernel.org/r/1eed6d69-d53d-9657-1fc9-c089be07f98c@linaro.org
Reported-by: Luis Machado <luis.machado@linaro.org>
Tested-by: Luis Machado <luis.machado@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/kernel/ptrace.c')
| -rw-r--r-- | arch/arm64/kernel/ptrace.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 057d4aa1af4d..22f9053b55b6 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1947,8 +1947,8 @@ static int valid_native_regs(struct user_pt_regs *regs) */ int valid_user_regs(struct user_pt_regs *regs, struct task_struct *task) { - if (!test_tsk_thread_flag(task, TIF_SINGLESTEP)) - regs->pstate &= ~DBG_SPSR_SS; + /* https://lore.kernel.org/lkml/20191118131525.GA4180@willie-the-truck */ + user_regs_reset_single_step(regs, task); if (is_compat_thread(task_thread_info(task))) return valid_compat_regs(regs); |