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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id b185sm42002pfg.14.2019.09.16.14.32.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Sep 2019 14:32:57 -0700 (PDT) Date: Mon, 16 Sep 2019 14:32:56 -0700 From: Kees Cook To: Randy Dunlap Cc: Matthew Wilcox , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] usercopy: Skip HIGHMEM page checking Message-ID: <201909161431.E69B29A0@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When running on a system with >512MB RAM with a 32-bit kernel built with: CONFIG_DEBUG_VIRTUAL=y CONFIG_HIGHMEM=y CONFIG_HARDENED_USERCOPY=y all execve()s will fail due to argv copying into kmap()ed pages, and on usercopy checking the calls ultimately of virt_to_page() will be looking for "bad" kmap (highmem) pointers due to CONFIG_DEBUG_VIRTUAL=y: ------------[ cut here ]------------ kernel BUG at ../arch/x86/mm/physaddr.c:83! invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.3.0-rc8 #6 Hardware name: Dell Inc. Inspiron 1318/0C236D, BIOS A04 01/15/2009 EIP: __phys_addr+0xaf/0x100 ... Call Trace: __check_object_size+0xaf/0x3c0 ? __might_sleep+0x80/0xa0 copy_strings+0x1c2/0x370 copy_strings_kernel+0x2b/0x40 __do_execve_file+0x4ca/0x810 ? kmem_cache_alloc+0x1c7/0x370 do_execve+0x1b/0x20 ... fs/exec.c: kaddr = kmap(kmapped_page); ... if (copy_from_user(kaddr+offset, str, bytes_to_copy)) ... Without CONFIG_DEBUG_VIRTUAL=y, these pages are effectively ignored, so now we do the same explicitly: detect and ignore kmap pages, instead of tripping over the check later. Reported-by: Randy Dunlap Fixes: f5509cc18daa ("mm: Hardened usercopy") Cc: Matthew Wilcox Cc: stable@vger.kernel.org Signed-off-by: Kees Cook --- Randy, I dropped your other Tested-by, since this is a different approach. I would expect the results to be identical (i.e. my testing shows it works), but I didn't want to assume. :) --- include/linux/highmem.h | 7 +++++++ mm/highmem.c | 2 +- mm/usercopy.c | 3 ++- 3 files changed, 10 insertions(+), 2 deletions(-) diff --git a/include/linux/highmem.h b/include/linux/highmem.h index ea5cdbd8c2c3..c881698b8023 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -64,12 +64,19 @@ static inline void totalhigh_pages_set(long val) void kmap_flush_unused(void); +static inline bool is_kmap(unsigned long addr) +{ + return (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)); +} + struct page *kmap_to_page(void *addr); #else /* CONFIG_HIGHMEM */ static inline unsigned int nr_free_highpages(void) { return 0; } +static inline bool is_kmap(unsigned long addr) { return false; } + static inline struct page *kmap_to_page(void *addr) { return virt_to_page(addr); diff --git a/mm/highmem.c b/mm/highmem.c index 107b10f9878e..e99eca4f63fa 100644 --- a/mm/highmem.c +++ b/mm/highmem.c @@ -151,7 +151,7 @@ struct page *kmap_to_page(void *vaddr) { unsigned long addr = (unsigned long)vaddr; - if (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)) { + if (is_kmap(addr)) { int i = PKMAP_NR(addr); return pte_page(pkmap_page_table[i]); } diff --git a/mm/usercopy.c b/mm/usercopy.c index 98e924864554..924e634cc95d 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -11,6 +11,7 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include +#include #include #include #include @@ -224,7 +225,7 @@ static inline void check_heap_object(const void *ptr, unsigned long n, { struct page *page; - if (!virt_addr_valid(ptr)) + if (!virt_addr_valid(ptr) || is_kmap((unsigned long)ptr)) return; page = virt_to_head_page(ptr); -- 2.17.1 -- Kees Cook