| Message ID | 20220701142310.2188015-19-glider@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Add KernelMemorySanitizer infrastructure | expand |
On Fri, 1 Jul 2022 at 16:24, Alexander Potapenko <glider@google.com> wrote: > > To avoid false positives, KMSAN needs to unpoison the data copied from > the userspace. To detect infoleaks - check the memory buffer passed to > copy_to_user(). > > Signed-off-by: Alexander Potapenko <glider@google.com> Reviewed-by: Marco Elver <elver@google.com> With the code simplification below. [...] > --- a/mm/kmsan/hooks.c > +++ b/mm/kmsan/hooks.c > @@ -212,6 +212,44 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end) > } > EXPORT_SYMBOL(kmsan_iounmap_page_range); > > +void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy, > + size_t left) > +{ > + unsigned long ua_flags; > + > + if (!kmsan_enabled || kmsan_in_runtime()) > + return; > + /* > + * At this point we've copied the memory already. It's hard to check it > + * before copying, as the size of actually copied buffer is unknown. > + */ > + > + /* copy_to_user() may copy zero bytes. No need to check. */ > + if (!to_copy) > + return; > + /* Or maybe copy_to_user() failed to copy anything. */ > + if (to_copy <= left) > + return; > + > + ua_flags = user_access_save(); > + if ((u64)to < TASK_SIZE) { > + /* This is a user memory access, check it. */ > + kmsan_internal_check_memory((void *)from, to_copy - left, to, > + REASON_COPY_TO_USER); This could just do "} else {" and the stuff below, and would result in simpler code with no explicit "return" and no duplicated user_access_restore(). > + user_access_restore(ua_flags); > + return; > + } > + /* Otherwise this is a kernel memory access. This happens when a compat > + * syscall passes an argument allocated on the kernel stack to a real > + * syscall. > + * Don't check anything, just copy the shadow of the copied bytes. > + */ > + kmsan_internal_memmove_metadata((void *)to, (void *)from, > + to_copy - left); > + user_access_restore(ua_flags); > +} > +EXPORT_SYMBOL(kmsan_copy_to_user);
On Tue, Jul 12, 2022 at 3:52 PM Marco Elver <elver@google.com> wrote: > > On Fri, 1 Jul 2022 at 16:24, Alexander Potapenko <glider@google.com> wrote: > > > > To avoid false positives, KMSAN needs to unpoison the data copied from > > the userspace. To detect infoleaks - check the memory buffer passed to > > copy_to_user(). > > > > Signed-off-by: Alexander Potapenko <glider@google.com> > > Reviewed-by: Marco Elver <elver@google.com> > > With the code simplification below. > > [...] > > --- a/mm/kmsan/hooks.c > > +++ b/mm/kmsan/hooks.c > > @@ -212,6 +212,44 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end) > > } > > EXPORT_SYMBOL(kmsan_iounmap_page_range); > > > > +void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy, > > + size_t left) > > +{ > > + unsigned long ua_flags; > > + > > + if (!kmsan_enabled || kmsan_in_runtime()) > > + return; > > + /* > > + * At this point we've copied the memory already. It's hard to check it > > + * before copying, as the size of actually copied buffer is unknown. > > + */ > > + > > + /* copy_to_user() may copy zero bytes. No need to check. */ > > + if (!to_copy) > > + return; > > + /* Or maybe copy_to_user() failed to copy anything. */ > > + if (to_copy <= left) > > + return; > > + > > + ua_flags = user_access_save(); > > + if ((u64)to < TASK_SIZE) { > > + /* This is a user memory access, check it. */ > > + kmsan_internal_check_memory((void *)from, to_copy - left, to, > > + REASON_COPY_TO_USER); > > This could just do "} else {" and the stuff below, and would result in > simpler code with no explicit "return" and no duplicated > user_access_restore(). Sounds good, will do.
diff --git a/include/linux/instrumented.h b/include/linux/instrumented.h index ee8f7d17d34f5..c73c1b19e9227 100644 --- a/include/linux/instrumented.h +++ b/include/linux/instrumented.h @@ -2,7 +2,7 @@ /* * This header provides generic wrappers for memory access instrumentation that - * the compiler cannot emit for: KASAN, KCSAN. + * the compiler cannot emit for: KASAN, KCSAN, KMSAN. */ #ifndef _LINUX_INSTRUMENTED_H #define _LINUX_INSTRUMENTED_H @@ -10,6 +10,7 @@ #include <linux/compiler.h> #include <linux/kasan-checks.h> #include <linux/kcsan-checks.h> +#include <linux/kmsan-checks.h> #include <linux/types.h> /** @@ -117,6 +118,7 @@ instrument_copy_to_user(void __user *to, const void *from, unsigned long n) { kasan_check_read(from, n); kcsan_check_read(from, n); + kmsan_copy_to_user(to, from, n, 0); } /** @@ -151,6 +153,7 @@ static __always_inline void instrument_copy_from_user_after(const void *to, const void __user *from, unsigned long n, unsigned long left) { + kmsan_unpoison_memory(to, n - left); } #endif /* _LINUX_INSTRUMENTED_H */ diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h index a6522a0c28df9..c4cae333deec5 100644 --- a/include/linux/kmsan-checks.h +++ b/include/linux/kmsan-checks.h @@ -46,6 +46,21 @@ void kmsan_unpoison_memory(const void *address, size_t size); */ void kmsan_check_memory(const void *address, size_t size); +/** + * kmsan_copy_to_user() - Notify KMSAN about a data transfer to userspace. + * @to: destination address in the userspace. + * @from: source address in the kernel. + * @to_copy: number of bytes to copy. + * @left: number of bytes not copied. + * + * If this is a real userspace data transfer, KMSAN checks the bytes that were + * actually copied to ensure there was no information leak. If @to belongs to + * the kernel space (which is possible for compat syscalls), KMSAN just copies + * the metadata. + */ +void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy, + size_t left); + #else static inline void kmsan_poison_memory(const void *address, size_t size, @@ -58,6 +73,10 @@ static inline void kmsan_unpoison_memory(const void *address, size_t size) static inline void kmsan_check_memory(const void *address, size_t size) { } +static inline void kmsan_copy_to_user(void __user *to, const void *from, + size_t to_copy, size_t left) +{ +} #endif diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c index 43a529569053d..1cdb4420977f1 100644 --- a/mm/kmsan/hooks.c +++ b/mm/kmsan/hooks.c @@ -212,6 +212,44 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end) } EXPORT_SYMBOL(kmsan_iounmap_page_range); +void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy, + size_t left) +{ + unsigned long ua_flags; + + if (!kmsan_enabled || kmsan_in_runtime()) + return; + /* + * At this point we've copied the memory already. It's hard to check it + * before copying, as the size of actually copied buffer is unknown. + */ + + /* copy_to_user() may copy zero bytes. No need to check. */ + if (!to_copy) + return; + /* Or maybe copy_to_user() failed to copy anything. */ + if (to_copy <= left) + return; + + ua_flags = user_access_save(); + if ((u64)to < TASK_SIZE) { + /* This is a user memory access, check it. */ + kmsan_internal_check_memory((void *)from, to_copy - left, to, + REASON_COPY_TO_USER); + user_access_restore(ua_flags); + return; + } + /* Otherwise this is a kernel memory access. This happens when a compat + * syscall passes an argument allocated on the kernel stack to a real + * syscall. + * Don't check anything, just copy the shadow of the copied bytes. + */ + kmsan_internal_memmove_metadata((void *)to, (void *)from, + to_copy - left); + user_access_restore(ua_flags); +} +EXPORT_SYMBOL(kmsan_copy_to_user); + /* Functions from kmsan-checks.h follow. */ void kmsan_poison_memory(const void *address, size_t size, gfp_t flags) {
To avoid false positives, KMSAN needs to unpoison the data copied from the userspace. To detect infoleaks - check the memory buffer passed to copy_to_user(). Signed-off-by: Alexander Potapenko <glider@google.com> --- v2: -- move implementation of kmsan_copy_to_user() here Link: https://linux-review.googlesource.com/id/I43e93b9c02709e6be8d222342f1b044ac8bdbaaf --- include/linux/instrumented.h | 5 ++++- include/linux/kmsan-checks.h | 19 ++++++++++++++++++ mm/kmsan/hooks.c | 38 ++++++++++++++++++++++++++++++++++++ 3 files changed, 61 insertions(+), 1 deletion(-)