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author | Kees Cook <keescook@chromium.org> | 2015-08-12 17:55:19 -0700 |
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committer | Ingo Molnar <mingo@kernel.org> | 2015-09-20 10:31:06 +0200 |
commit | 3dc33bd30f3e1c1bcaaafa3482737694debf0f0b (patch) | |
tree | cd60ac8be186562ed7fd892ce2f1d016b8166702 /arch/x86/Kconfig | |
parent | c25be94f2870bf75552a41ad8b15f756e19ffb1d (diff) | |
download | linux-3dc33bd30f3e1c1bcaaafa3482737694debf0f0b.tar.gz linux-3dc33bd30f3e1c1bcaaafa3482737694debf0f0b.tar.bz2 linux-3dc33bd30f3e1c1bcaaafa3482737694debf0f0b.zip |
x86/entry/vsyscall: Add CONFIG to control default
Most modern systems can run with vsyscall=none. In an effort to
provide a way for build-time defaults to lack legacy settings,
this adds a new CONFIG to select the type of vsyscall mapping to
use, similar to the existing "vsyscall" command line parameter.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150813005519.GA11696@www.outflux.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/Kconfig')
-rw-r--r-- | arch/x86/Kconfig | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 328c8352480c..9bfb9e15a6e8 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2042,6 +2042,55 @@ config COMPAT_VDSO If unsure, say N: if you are compiling your own kernel, you are unlikely to be using a buggy version of glibc. +choice + prompt "vsyscall table for legacy applications" + depends on X86_64 + default LEGACY_VSYSCALL_EMULATE + help + Legacy user code that does not know how to find the vDSO expects + to be able to issue three syscalls by calling fixed addresses in + kernel space. Since this location is not randomized with ASLR, + it can be used to assist security vulnerability exploitation. + + This setting can be changed at boot time via the kernel command + line parameter vsyscall=[native|emulate|none]. + + On a system with recent enough glibc (2.14 or newer) and no + static binaries, you can say None without a performance penalty + to improve security. + + If unsure, select "Emulate". + + config LEGACY_VSYSCALL_NATIVE + bool "Native" + help + Actual executable code is located in the fixed vsyscall + address mapping, implementing time() efficiently. Since + this makes the mapping executable, it can be used during + security vulnerability exploitation (traditionally as + ROP gadgets). This configuration is not recommended. + + config LEGACY_VSYSCALL_EMULATE + bool "Emulate" + help + The kernel traps and emulates calls into the fixed + vsyscall address mapping. This makes the mapping + non-executable, but it still contains known contents, + which could be used in certain rare security vulnerability + exploits. This configuration is recommended when userspace + still uses the vsyscall area. + + config LEGACY_VSYSCALL_NONE + bool "None" + help + There will be no vsyscall mapping at all. This will + eliminate any risk of ASLR bypass due to the vsyscall + fixed address mapping. Attempts to use the vsyscalls + will be reported to dmesg, so that either old or + malicious userspace programs can be identified. + +endchoice + config CMDLINE_BOOL bool "Built-in kernel command line" ---help--- |