From 5cec93c216db77c45f7ce970d46283bcb1933884 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sun, 5 Jun 2011 13:50:24 -0400 Subject: x86-64: Emulate legacy vsyscalls There's a fair amount of code in the vsyscall page. It contains a syscall instruction (in the gettimeofday fallback) and who knows what will happen if an exploit jumps into the middle of some other code. Reduce the risk by replacing the vsyscalls with short magic incantations that cause the kernel to emulate the real vsyscalls. These incantations are useless if entered in the middle. This causes vsyscalls to be a little more expensive than real syscalls. Fortunately sensible programs don't use them. The only exception is time() which is still called by glibc through the vsyscall - but calling time() millions of times per second is not sensible. glibc has this fixed in the development tree. This patch is not perfect: the vread_tsc and vread_hpet functions are still at a fixed address. Fixing that might involve making alternative patching work in the vDSO. Signed-off-by: Andy Lutomirski Acked-by: Linus Torvalds Cc: Jesper Juhl Cc: Borislav Petkov Cc: Arjan van de Ven Cc: Jan Beulich Cc: richard -rw- weinberger Cc: Mikael Pettersson Cc: Andi Kleen Cc: Brian Gerst Cc: Louis Rilling Cc: Valdis.Kletnieks@vt.edu Cc: pageexec@freemail.hu Link: http://lkml.kernel.org/r/e64e1b3c64858820d12c48fa739efbd1485e79d5.1307292171.git.luto@mit.edu [ Removed the CONFIG option - it's simpler to just do it unconditionally. Tidied up the code as well. ] Signed-off-by: Ingo Molnar --- arch/x86/include/asm/vsyscall.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'arch/x86/include/asm/vsyscall.h') diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h index d55597351f6a..bb710cb0cdc1 100644 --- a/arch/x86/include/asm/vsyscall.h +++ b/arch/x86/include/asm/vsyscall.h @@ -31,6 +31,18 @@ extern struct timezone sys_tz; extern void map_vsyscall(void); +/* Emulation */ + +static inline bool is_vsyscall_entry(unsigned long addr) +{ + return (addr & ~0xC00UL) == VSYSCALL_START; +} + +static inline int vsyscall_entry_nr(unsigned long addr) +{ + return (addr & 0xC00UL) >> 10; +} + #endif /* __KERNEL__ */ #endif /* _ASM_X86_VSYSCALL_H */ -- cgit v1.2.3