From 4a3127693001c61a21d1ce680db6340623f52e93 Mon Sep 17 00:00:00 2001 From: Arjan van de Ven Date: Wed, 30 Sep 2009 13:05:23 +0200 Subject: [PATCH] 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(-) 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(), -- 2.20.1