From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> The kernel can use to allocate executable memory. The only supported way to do that is via __vmalloc_node_range() with the executable bit set in the prot argument. (vmap() resets the bit via pgprot_nx()). Once tag-based KASAN modes start tagging vmalloc allocations, executing code from such allocations will lead to the PC register getting a tag, which is not tolerated by the kernel. Don't tag the allocation if page protections allow execution. Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> --- Changes v2->v3: - Add this patch. --- include/linux/kasan.h | 1 + mm/kasan/hw_tags.c | 7 +++++++ mm/kasan/shadow.c | 7 +++++++ mm/vmalloc.c | 10 +++++++--- 4 files changed, 22 insertions(+), 3 deletions(-) diff --git a/include/linux/kasan.h b/include/linux/kasan.h index 499f1573dba4..11f29c121bee 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -30,6 +30,7 @@ typedef unsigned int __bitwise kasan_vmalloc_flags_t; #define KASAN_VMALLOC_NONE 0x00u #define KASAN_VMALLOC_INIT 0x01u #define KASAN_VMALLOC_VM_ALLOC 0x02u +#define KASAN_VMALLOC_NOEXEC 0x04u #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS) diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c index de564a6187e1..bbcf6f914490 100644 --- a/mm/kasan/hw_tags.c +++ b/mm/kasan/hw_tags.c @@ -246,6 +246,13 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size, if (!(flags & KASAN_VMALLOC_VM_ALLOC)) return (void *)start; + /* + * Don't tag executable memory. + * The kernel doesn't tolerate having the PC register tagged. + */ + if (!(flags & KASAN_VMALLOC_NOEXEC)) + return (void *)start; + tag = kasan_random_tag(); start = set_tag(start, tag); diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c index b958babc8fed..d86ab0a9dcc3 100644 --- a/mm/kasan/shadow.c +++ b/mm/kasan/shadow.c @@ -488,6 +488,13 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size, if (!is_vmalloc_or_module_addr(start)) return (void *)start; + /* + * Don't tag executable memory. + * The kernel doesn't tolerate having the PC register tagged. + */ + if (!(flags & KASAN_VMALLOC_NOEXEC)) + return (void *)start; + start = set_tag(start, kasan_random_tag()); kasan_unpoison(start, size, false); return (void *)start; diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 4171778922cc..75afd6c9bc3d 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2219,7 +2219,7 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node) * With hardware tag-based KASAN, marking is skipped for * non-VM_ALLOC mappings, see __kasan_unpoison_vmalloc(). */ - mem = kasan_unpoison_vmalloc(mem, size, KASAN_VMALLOC_NONE); + mem = kasan_unpoison_vmalloc(mem, size, KASAN_VMALLOC_NOEXEC); return mem; } @@ -2458,7 +2458,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size, */ if (!(flags & VM_ALLOC)) area->addr = kasan_unpoison_vmalloc(area->addr, requested_size, - KASAN_VMALLOC_NONE); + KASAN_VMALLOC_NOEXEC); return area; } @@ -3133,10 +3133,14 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align, * (except for the should_skip_init() check) to make sure that memory * is initialized under the same conditions regardless of the enabled * KASAN mode. + * Tag-based KASAN modes only assign tags to non-executable + * allocations, see __kasan_unpoison_vmalloc(). */ kasan_flags = KASAN_VMALLOC_VM_ALLOC; if (!want_init_on_free() && want_init_on_alloc(gfp_mask)) kasan_flags |= KASAN_VMALLOC_INIT; + if (pgprot_val(prot) == pgprot_val(pgprot_nx(prot))) + kasan_flags |= KASAN_VMALLOC_NOEXEC; addr = kasan_unpoison_vmalloc(addr, real_size, kasan_flags); /* @@ -3844,7 +3848,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, for (area = 0; area < nr_vms; area++) vms[area]->addr = kasan_unpoison_vmalloc(vms[area]->addr, vms[area]->size, - KASAN_VMALLOC_NONE); + KASAN_VMALLOC_NOEXEC); kfree(vas); return vms; -- 2.25.1
