When calling KMSAN-instrumented functions from non-instrumented functions, function parameters may not be initialized properly, leading to false positive reports. In particular, this happens all the time when calling interrupt handlers from `noinstr` IDT entries. We introduce instrumentation_begin_with_regs(), which calls instrumentation_begin() and notifies KMSAN about the beginning of the potentially instrumented region by calling kmsan_instrumentation_begin(), which: - wipes the current KMSAN state at the beginning of the region, ensuring that the first call of an instrumented function receives initialized parameters (this is a pretty good approximation of having all other instrumented functions receive initialized parameters); - unpoisons the `struct pt_regs` set up by the non-instrumented assembly code. Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> --- Link: https://linux-review.googlesource.com/id/I0f5e3372e00bd5fe25ddbf286f7260aae9011858 --- include/linux/instrumentation.h | 6 ++++++ include/linux/kmsan.h | 11 +++++++++++ mm/kmsan/hooks.c | 16 ++++++++++++++++ 3 files changed, 33 insertions(+) diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h index 24359b4a96053..3bbce9d556381 100644 --- a/include/linux/instrumentation.h +++ b/include/linux/instrumentation.h @@ -15,6 +15,11 @@ }) #define instrumentation_begin() __instrumentation_begin(__COUNTER__) +#define instrumentation_begin_with_regs(regs) do { \ + __instrumentation_begin(__COUNTER__); \ + kmsan_instrumentation_begin(regs); \ +} while (0) + /* * Because instrumentation_{begin,end}() can nest, objtool validation considers * _begin() a +1 and _end() a -1 and computes a sum over the instructions. @@ -55,6 +60,7 @@ #define instrumentation_end() __instrumentation_end(__COUNTER__) #else # define instrumentation_begin() do { } while(0) +# define instrumentation_begin_with_regs(regs) kmsan_instrumentation_begin(regs) # define instrumentation_end() do { } while(0) #endif diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h index 55f976b721566..209a5a2192e22 100644 --- a/include/linux/kmsan.h +++ b/include/linux/kmsan.h @@ -247,6 +247,13 @@ void kmsan_handle_dma_sg(struct scatterlist *sg, int nents, */ void kmsan_handle_urb(const struct urb *urb, bool is_out); +/** + * kmsan_instrumentation_begin() - handle instrumentation_begin(). + * @regs: pointer to struct pt_regs that non-instrumented code passes to + * instrumented code. + */ +void kmsan_instrumentation_begin(struct pt_regs *regs); + #else static inline void kmsan_init_shadow(void) @@ -343,6 +350,10 @@ static inline void kmsan_handle_urb(const struct urb *urb, bool is_out) { } +static inline void kmsan_instrumentation_begin(struct pt_regs *regs) +{ +} + #endif #endif /* _LINUX_KMSAN_H */ diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c index 9aecbf2825837..c20d105c143c1 100644 --- a/mm/kmsan/hooks.c +++ b/mm/kmsan/hooks.c @@ -366,3 +366,19 @@ void kmsan_check_memory(const void *addr, size_t size) REASON_ANY); } EXPORT_SYMBOL(kmsan_check_memory); + +void kmsan_instrumentation_begin(struct pt_regs *regs) +{ + struct kmsan_context_state *state = &kmsan_get_context()->cstate; + + if (state) + __memset(state, 0, sizeof(struct kmsan_context_state)); + if (!kmsan_enabled || !regs) + return; + /* + * @regs may reside in cpu_entry_area, for which KMSAN does not allocate + * metadata. Do not force an error in that case. + */ + kmsan_internal_unpoison_memory(regs, sizeof(*regs), /*checked*/ false); +} +EXPORT_SYMBOL(kmsan_instrumentation_begin); -- 2.36.0.rc2.479.g8af0fa9b8e-goog
