From 9f0cf4adb6aa0bfccf675c938124e68f7f06349d Mon Sep 17 00:00:00 2001 From: Arjan van de Ven Date: Sat, 26 Sep 2009 14:33:01 +0200 Subject: x86: Use __builtin_object_size() to validate the buffer size for copy_from_user() gcc (4.x) supports the __builtin_object_size() builtin, which reports the size of an object that a pointer point to, when known at compile time. If the buffer size is not known at compile time, a constant -1 is returned. This patch uses this feature to add a sanity check to copy_from_user(); if the target buffer is known to be smaller than the copy size, the copy is aborted and a WARNing is emitted in memory debug mode. These extra checks compile away when the object size is not known, or if both the buffer size and the copy length are constants. Signed-off-by: Arjan van de Ven LKML-Reference: <20090926143301.2c396b94@infradead.org> Signed-off-by: Ingo Molnar --- include/linux/compiler.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux/compiler.h') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 04fb5135b4e1..8e54108688f9 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -266,6 +266,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b)) #endif +/* Compile time object size, -1 for unknown */ +#ifndef __compiletime_object_size +# define __compiletime_object_size(obj) -1 +#endif /* * Prevent the compiler from merging or refetching accesses. The compiler * is also forbidden from reordering successive instances of ACCESS_ONCE(), -- cgit v1.2.3 From 4a3127693001c61a21d1ce680db6340623f52e93 Mon Sep 17 00:00:00 2001 From: Arjan van de Ven Date: Wed, 30 Sep 2009 13:05:23 +0200 Subject: x86: Turn the copy_from_user check into an (optional) compile time warning A previous patch added the buffer size check to copy_from_user(). One of the things learned from analyzing the result of the previous patch is that in general, gcc is really good at proving that the code contains sufficient security checks to not need to do a runtime check. But that for those cases where gcc could not prove this, there was a relatively high percentage of real security issues. This patch turns the case of "gcc cannot prove" into a compile time warning, as long as a sufficiently new gcc is in use that supports this. The objective is that these warnings will trigger developers checking new cases out before a security hole enters a linux kernel release. Signed-off-by: Arjan van de Ven Cc: Linus Torvalds Cc: "David S. Miller" Cc: James Morris Cc: Jan Beulich LKML-Reference: <20090930130523.348ae6c4@infradead.org> Signed-off-by: Ingo Molnar --- arch/x86/include/asm/uaccess_32.h | 12 +++++++++--- arch/x86/lib/usercopy_32.c | 6 ++++++ include/linux/compiler-gcc4.h | 3 +++ include/linux/compiler.h | 4 ++++ 4 files changed, 22 insertions(+), 3 deletions(-) (limited to 'include/linux/compiler.h') diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h index 582d6aef7417..952f9e793c3e 100644 --- a/arch/x86/include/asm/uaccess_32.h +++ b/arch/x86/include/asm/uaccess_32.h @@ -191,6 +191,13 @@ unsigned long __must_check _copy_from_user(void *to, const void __user *from, unsigned long n); + +extern void copy_from_user_overflow(void) +#ifdef CONFIG_DEBUG_STACKOVERFLOW + __compiletime_warning("copy_from_user() buffer size is not provably correct") +#endif +; + static inline unsigned long __must_check copy_from_user(void *to, const void __user *from, unsigned long n) @@ -200,10 +207,9 @@ static inline unsigned long __must_check copy_from_user(void *to, if (likely(sz == -1 || sz >= n)) ret = _copy_from_user(to, from, n); -#ifdef CONFIG_DEBUG_VM else - WARN(1, "Buffer overflow detected!\n"); -#endif + copy_from_user_overflow(); + return ret; } diff --git a/arch/x86/lib/usercopy_32.c b/arch/x86/lib/usercopy_32.c index 8498684e45b0..e218d5df85ff 100644 --- a/arch/x86/lib/usercopy_32.c +++ b/arch/x86/lib/usercopy_32.c @@ -883,3 +883,9 @@ _copy_from_user(void *to, const void __user *from, unsigned long n) return n; } EXPORT_SYMBOL(_copy_from_user); + +void copy_from_user_overflow(void) +{ + WARN(1, "Buffer overflow detected!\n"); +} +EXPORT_SYMBOL(copy_from_user_overflow); diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h index a3aef5d55dba..f1709c1f9eae 100644 --- a/include/linux/compiler-gcc4.h +++ b/include/linux/compiler-gcc4.h @@ -39,3 +39,6 @@ #endif #define __compiletime_object_size(obj) __builtin_object_size(obj, 0) +#if __GNUC_MINOR__ >= 4 +#define __compiletime_warning(message) __attribute__((warning(message))) +#endif diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 8e54108688f9..950356311f12 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -270,6 +270,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); #ifndef __compiletime_object_size # define __compiletime_object_size(obj) -1 #endif +#ifndef __compiletime_warning +# define __compiletime_warning(message) +#endif + /* * Prevent the compiler from merging or refetching accesses. The compiler * is also forbidden from reordering successive instances of ACCESS_ONCE(), -- cgit v1.2.3 From 63312b6a6faae3f2e5577f2b001e3b504f10a2aa Mon Sep 17 00:00:00 2001 From: Arjan van de Ven Date: Fri, 2 Oct 2009 07:50:50 -0700 Subject: x86: Add a Kconfig option to turn the copy_from_user warnings into errors MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit For automated testing it is useful to have the option to turn the warnings on copy_from_user() etc checks into errors: In function ‘copy_from_user’, inlined from ‘fd_copyin’ at drivers/block/floppy.c:3080, inlined from ‘fd_ioctl’ at drivers/block/floppy.c:3503: linux/arch/x86/include/asm/uaccess_32.h:213: error: call to ‘copy_from_user_overflow’ declared with attribute error: copy_from_user buffer size is not provably correct Signed-off-by: Arjan van de Ven Cc: Linus Torvalds Cc: Andrew Morton LKML-Reference: <20091002075050.4e9f7641@infradead.org> Signed-off-by: Ingo Molnar --- arch/x86/Kconfig.debug | 14 ++++++++++++++ arch/x86/include/asm/uaccess_32.h | 4 +++- include/linux/compiler-gcc4.h | 1 + include/linux/compiler.h | 3 +++ 4 files changed, 21 insertions(+), 1 deletion(-) (limited to 'include/linux/compiler.h') diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index d105f29bb6bb..1bd2e36f1538 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -287,4 +287,18 @@ config OPTIMIZE_INLINING If unsure, say N. +config DEBUG_STRICT_USER_COPY_CHECKS + bool "Strict copy size checks" + depends on DEBUG_KERNEL + ---help--- + Enabling this option turns a certain set of sanity checks for user + copy operations into compile time failures. + + The copy_from_user() etc checks are there to help test if there + are sufficient security checks on the length argument of + the copy operation, by having gcc prove that the argument is + within bounds. + + If unsure, or if you run an older (pre 4.4) gcc, say N. + endmenu diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h index 952f9e793c3e..0c9825e97f36 100644 --- a/arch/x86/include/asm/uaccess_32.h +++ b/arch/x86/include/asm/uaccess_32.h @@ -193,7 +193,9 @@ unsigned long __must_check _copy_from_user(void *to, extern void copy_from_user_overflow(void) -#ifdef CONFIG_DEBUG_STACKOVERFLOW +#ifdef CONFIG_DEBUG_STRICT_USER_COPY_CHECKS + __compiletime_error("copy_from_user() buffer size is not provably correct") +#else __compiletime_warning("copy_from_user() buffer size is not provably correct") #endif ; diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h index f1709c1f9eae..77542c57e20a 100644 --- a/include/linux/compiler-gcc4.h +++ b/include/linux/compiler-gcc4.h @@ -41,4 +41,5 @@ #define __compiletime_object_size(obj) __builtin_object_size(obj, 0) #if __GNUC_MINOR__ >= 4 #define __compiletime_warning(message) __attribute__((warning(message))) +#define __compiletime_error(message) __attribute__((error(message))) #endif diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 950356311f12..88fd4b673cb4 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -273,6 +273,9 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); #ifndef __compiletime_warning # define __compiletime_warning(message) #endif +#ifndef __compiletime_error +# define __compiletime_error(message) +#endif /* * Prevent the compiler from merging or refetching accesses. The compiler -- cgit v1.2.3