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Subject[PATCH 13/14] arm64: add on_accessible_stack()
Date
Both unwind_frame() and dump_backtrace() try to check whether a stack
address is sane to access, with very similar logic. Both will need
updating in order to handle overflow stacks.

Factor out this logic into a helper, so that we can avoid further
duplication when we add overflow stacks.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
---
arch/arm64/include/asm/stacktrace.h | 16 ++++++++++++++++
arch/arm64/kernel/stacktrace.c | 7 +------
arch/arm64/kernel/traps.c | 3 +--
3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 4c68d8a..92ddb6d 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -57,4 +57,20 @@ static inline bool on_task_stack(struct task_struct *tsk, unsigned long sp)
return (low <= sp && sp < high);
}

+/*
+ * We can only safely access per-cpu stacks from current in a non-preemptible
+ * context.
+ */
+static inline bool on_accessible_stack(struct task_struct *tsk, unsigned long sp)
+{
+ if (on_task_stack(tsk, sp))
+ return true;
+ if (tsk != current || preemptible())
+ return false;
+ if (on_irq_stack(sp))
+ return true;
+
+ return false;
+}
+
#endif /* __ASM_STACKTRACE_H */
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 54f3463..d9b80eb 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -50,12 +50,7 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
if (!tsk)
tsk = current;

- /*
- * Switching between stacks is valid when tracing current and in
- * non-preemptible context.
- */
- if (!(tsk == current && !preemptible() && on_irq_stack(fp)) &&
- !on_task_stack(tsk, fp))
+ if (!on_accessible_stack(tsk, fp))
return -EINVAL;

frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 9633773..d01c598 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -193,8 +193,7 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
if (in_entry_text(frame.pc)) {
stack = frame.fp - offsetof(struct pt_regs, stackframe);

- if (on_task_stack(tsk, stack) ||
- (tsk == current && !preemptible() && on_irq_stack(stack)))
+ if (on_accessible_stack(tsk, stack))
dump_mem("", "Exception stack", stack,
stack + sizeof(struct pt_regs));
}
--
1.9.1
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