Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964993Ab2EOCRC (ORCPT ); Mon, 14 May 2012 22:17:02 -0400 Received: from mail1.windriver.com ([147.11.146.13]:52805 "EHLO mail1.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964866Ab2EOCQG (ORCPT ); Mon, 14 May 2012 22:16:06 -0400 From: Paul Gortmaker To: , Subject: [34-longterm 009/179] x86, 64-bit: Fix copy_[to/from]_user() checks for the userspace address limit Date: Mon, 14 May 2012 22:11:45 -0400 Message-ID: <1337048075-6132-10-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.7.9.6 In-Reply-To: <1337048075-6132-1-git-send-email-paul.gortmaker@windriver.com> References: <1337048075-6132-1-git-send-email-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4491 Lines: 129 From: Jiri Olsa ------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. ------------------- commit 26afb7c661080ae3f1f13ddf7f0c58c4f931c22b upstream. As reported in BZ #30352: https://bugzilla.kernel.org/show_bug.cgi?id=30352 there's a kernel bug related to reading the last allowed page on x86_64. The _copy_to_user() and _copy_from_user() functions use the following check for address limit: if (buf + size >= limit) fail(); while it should be more permissive: if (buf + size > limit) fail(); That's because the size represents the number of bytes being read/write from/to buf address AND including the buf address. So the copy function will actually never touch the limit address even if "buf + size == limit". Following program fails to use the last page as buffer due to the wrong limit check: #include #include #include #define PAGE_SIZE (4096) #define LAST_PAGE ((void*)(0x7fffffffe000)) int main() { int fds[2], err; void * ptr = mmap(LAST_PAGE, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0); assert(ptr == LAST_PAGE); err = socketpair(AF_LOCAL, SOCK_STREAM, 0, fds); assert(err == 0); err = send(fds[0], ptr, PAGE_SIZE, 0); perror("send"); assert(err == PAGE_SIZE); err = recv(fds[1], ptr, PAGE_SIZE, MSG_WAITALL); perror("recv"); assert(err == PAGE_SIZE); return 0; } The other place checking the addr limit is the access_ok() function, which is working properly. There's just a misleading comment for the __range_not_ok() macro - which this patch fixes as well. The last page of the user-space address range is a guard page and Brian Gerst observed that the guard page itself due to an erratum on K8 cpus (#121 Sequential Execution Across Non-Canonical Boundary Causes Processor Hang). However, the test code is using the last valid page before the guard page. The bug is that the last byte before the guard page can't be read because of the off-by-one error. The guard page is left in place. This bug would normally not show up because the last page is part of the process stack and never accessed via syscalls. Signed-off-by: Jiri Olsa Acked-by: Brian Gerst Acked-by: Linus Torvalds Link: http://lkml.kernel.org/r/1305210630-7136-1-git-send-email-jolsa@redhat.com Signed-off-by: Ingo Molnar Signed-off-by: Paul Gortmaker --- arch/x86/include/asm/uaccess.h | 2 +- arch/x86/lib/copy_user_64.S | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index abd3e0e..99f0ad7 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -42,7 +42,7 @@ * Returns 0 if the range is valid, nonzero otherwise. * * This is equivalent to the following test: - * (u33)addr + (u33)size >= (u33)current->addr_limit.seg (u65 for x86_64) + * (u33)addr + (u33)size > (u33)current->addr_limit.seg (u65 for x86_64) * * This needs 33-bit (65-bit for x86_64) arithmetic. We have a carry... */ diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S index 71100c9..a4899ae 100644 --- a/arch/x86/lib/copy_user_64.S +++ b/arch/x86/lib/copy_user_64.S @@ -72,7 +72,7 @@ ENTRY(_copy_to_user) addq %rdx,%rcx jc bad_to_user cmpq TI_addr_limit(%rax),%rcx - jae bad_to_user + ja bad_to_user ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string CFI_ENDPROC ENDPROC(_copy_to_user) @@ -85,7 +85,7 @@ ENTRY(_copy_from_user) addq %rdx,%rcx jc bad_from_user cmpq TI_addr_limit(%rax),%rcx - jae bad_from_user + ja bad_from_user ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string CFI_ENDPROC ENDPROC(_copy_from_user) -- 1.7.9.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/