Messages in this thread Patch in this message | | | From | Mark Rutland <> | Subject | [PATCH 7/8] stackleak: add on/off stack variants | Date | Mon, 25 Apr 2022 12:56:02 +0100 |
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The stackleak_erase() code dynamically handles being on a task stack or another stack. In most cases, this is a fixed property of the caller, which the caller is aware of, as an architecture might always return using the task stack, or might always return using a trampoline stack.
This patch adds stackleak_erase_on_task_stack() and stackleak_erase_off_task_stack() functions which callers can use to avoid on_thread_stack() check and associated redundant work when the calling stack is known. The existing stackleak_erase() is retained as a safe default.
There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Popov <alex.popov@linux.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Kees Cook <keescook@chromium.org> --- kernel/stackleak.c | 35 ++++++++++++++++++++++++++++++++--- 1 file changed, 32 insertions(+), 3 deletions(-)
diff --git a/kernel/stackleak.c b/kernel/stackleak.c index ba346d46218f5..4c3f82066d7fb 100644 --- a/kernel/stackleak.c +++ b/kernel/stackleak.c @@ -70,7 +70,7 @@ late_initcall(stackleak_sysctls_init); #define skip_erasing() false #endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */ -static __always_inline void __stackleak_erase(void) +static __always_inline void __stackleak_erase(bool on_task_stack) { const unsigned long task_stack_low = stackleak_task_low_bound(current); const unsigned long task_stack_high = stackleak_task_high_bound(current); @@ -106,7 +106,7 @@ static __always_inline void __stackleak_erase(void) * function has a fixed-size stack frame, and the current stack pointer * doesn't change while we write poison. */ - if (on_thread_stack()) + if (on_task_stack) erase_high = current_stack_pointer; else erase_high = task_stack_high; @@ -120,12 +120,41 @@ static __always_inline void __stackleak_erase(void) current->lowest_stack = task_stack_high; } +/* + * Erase and poison the portion of the task stack used since the last erase. + * Can be called from the task stack or an entry stack when the task stack is + * no longer in use. + */ asmlinkage void noinstr stackleak_erase(void) { if (skip_erasing()) return; - __stackleak_erase(); + __stackleak_erase(on_thread_stack()); +} + +/* + * Erase and poison the portion of the task stack used since the last erase. + * Can only be called from the task stack. + */ +asmlinkage void noinstr stackleak_erase_on_task_stack(void) +{ + if (skip_erasing()) + return; + + __stackleak_erase(true); +} + +/* + * Erase and poison the portion of the task stack used since the last erase. + * Can only be called from a stack other than the task stack. + */ +asmlinkage void noinstr stackleak_erase_off_task_stack(void) +{ + if (skip_erasing()) + return; + + __stackleak_erase(false); } void __used __no_caller_saved_registers noinstr stackleak_track_stack(void) -- 2.30.2
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