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Message-Id: <1515531365-37423-27-git-send-email-keescook@chromium.org> Date: Tue, 9 Jan 2018 12:55:55 -0800 From: Kees Cook <keescook@...omium.org> To: linux-kernel@...r.kernel.org Cc: Kees Cook <keescook@...omium.org>, David Windsor <dave@...lcore.net>, Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Andy Lutomirski <luto@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Alexander Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@...radead.org>, Christoph Lameter <cl@...ux.com>, "David S. Miller" <davem@...emloft.net>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, "Martin K. Petersen" <martin.petersen@...cle.com>, Paolo Bonzini <pbonzini@...hat.com>, Christian Borntraeger <borntraeger@...ibm.com>, Christoffer Dall <christoffer.dall@...aro.org>, Dave Kleikamp <dave.kleikamp@...cle.com>, Jan Kara <jack@...e.cz>, Luis de Bethencourt <luisbg@...nel.org>, Marc Zyngier <marc.zyngier@....com>, Rik van Riel <riel@...hat.com>, Matthew Garrett <mjg59@...gle.com>, linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org, netdev@...r.kernel.org, linux-mm@...ck.org, kernel-hardening@...ts.openwall.com Subject: [PATCH 26/36] fork: Define usercopy region in mm_struct slab caches From: David Windsor <dave@...lcore.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@...lcore.net> [kees: adjust commit log, split patch, provide usage trace] Cc: Ingo Molnar <mingo@...nel.org> Cc: Andrew Morton <akpm@...ux-foundation.org> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Andy Lutomirski <luto@...nel.org> Signed-off-by: Kees Cook <keescook@...omium.org> Acked-by: Rik van Riel <riel@...hat.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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