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authorWill Deacon <will@kernel.org>2020-02-13 15:06:26 +0300
committerWill Deacon <will@kernel.org>2020-07-16 13:41:21 +0300
commit3a5a4366cecc25daa300b9a9174f7fdd352b9068 (patch)
treecab8688b96d324ee0b110d0525679eee6f2a43e5 /arch/arm64/include
parentac2081cdc4d99c57f219c1a6171526e0fa0a6fff (diff)
downloadlinux-3a5a4366cecc25daa300b9a9174f7fdd352b9068.tar.xz
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/include')
-rw-r--r--arch/arm64/include/asm/debug-monitors.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h
index e5ceea213e39..0b298f48f5bf 100644
--- a/arch/arm64/include/asm/debug-monitors.h
+++ b/arch/arm64/include/asm/debug-monitors.h
@@ -109,6 +109,8 @@ void disable_debug_monitors(enum dbg_active_el el);
void user_rewind_single_step(struct task_struct *task);
void user_fastforward_single_step(struct task_struct *task);
+void user_regs_reset_single_step(struct user_pt_regs *regs,
+ struct task_struct *task);
void kernel_enable_single_step(struct pt_regs *regs);
void kernel_disable_single_step(void);