Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH 26/36] fork: Define usercopy region in mm_struct slab caches | Date | Tue, 9 Jan 2018 12:55:55 -0800 |
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From: David Windsor <dave@nullcore.net>
In support of usercopy hardening, this patch defines a region in the mm_struct slab caches in which userspace copy operations are allowed. Only the auxv field is copied to userspace.
cache object allocation: kernel/fork.c: #define allocate_mm() (kmem_cache_alloc(mm_cachep, GFP_KERNEL))
dup_mm(): ... mm = allocate_mm();
copy_mm(...): ... dup_mm();
copy_process(...): ... copy_mm(...)
_do_fork(...): ... copy_process(...)
example usage trace:
fs/binfmt_elf.c: create_elf_tables(...): ... elf_info = (elf_addr_t *)current->mm->saved_auxv; ... copy_to_user(..., elf_info, ei_index * sizeof(elf_addr_t))
load_elf_binary(...): ... create_elf_tables(...);
This region is known as the slab cache's usercopy region. Slab caches can now check that each dynamically sized copy operation involving cache-managed memory falls entirely within the slab's usercopy region.
This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY whitelisting code in the last public patch of grsecurity/PaX based on my understanding of the code. Changes or omissions from the original code are mine and don't reflect the original grsecurity/PaX code.
Signed-off-by: David Windsor <dave@nullcore.net> [kees: adjust commit log, split patch, provide usage trace] Cc: Ingo Molnar <mingo@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Andy Lutomirski <luto@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Rik van Riel <riel@redhat.com> --- kernel/fork.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/fork.c b/kernel/fork.c index 432eadf6b58c..82f2a0441d3b 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2225,9 +2225,11 @@ void __init proc_caches_init(void) * maximum number of CPU's we can ever have. The cpumask_allocation * is at the end of the structure, exactly for that reason. */ - mm_cachep = kmem_cache_create("mm_struct", + mm_cachep = kmem_cache_create_usercopy("mm_struct", sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, + offsetof(struct mm_struct, saved_auxv), + sizeof_field(struct mm_struct, saved_auxv), NULL); vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT); mmap_init(); -- 2.7.4
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