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 <luto@mit.edu>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jesper Juhl <jj@chaosbits.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Jan Beulich <JBeulich@novell.com>
Cc: richard -rw- weinberger <richard.weinberger@gmail.com>
Cc: Mikael Pettersson <mikpe@it.uu.se>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Louis Rilling <Louis.Rilling@kerlabs.com>
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 <mingo@elte.hu>
diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
index 6e976ee..a563c50 100644
--- a/arch/x86/include/asm/irq_vectors.h
+++ b/arch/x86/include/asm/irq_vectors.h
@@ -17,7 +17,8 @@
* Vectors 0 ... 31 : system traps and exceptions - hardcoded events
* Vectors 32 ... 127 : device interrupts
* Vector 128 : legacy int80 syscall interface
- * Vectors 129 ... INVALIDATE_TLB_VECTOR_START-1 : device interrupts
+ * Vector 204 : legacy x86_64 vsyscall emulation
+ * Vectors 129 ... INVALIDATE_TLB_VECTOR_START-1 except 204 : device interrupts
* Vectors INVALIDATE_TLB_VECTOR_START ... 255 : special interrupts
*
* 64-bit x86 has per CPU IDT tables, 32-bit has one shared IDT table.
@@ -50,6 +51,9 @@
#ifdef CONFIG_X86_32
# define SYSCALL_VECTOR 0x80
#endif
+#ifdef CONFIG_X86_64
+# define VSYSCALL_EMU_VECTOR 0xcc
+#endif
/*
* Vectors 0x30-0x3f are used for ISA interrupts.
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 0310da6..2bae0a5 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -1,6 +1,8 @@
#ifndef _ASM_X86_TRAPS_H
#define _ASM_X86_TRAPS_H
+#include <linux/kprobes.h>
+
#include <asm/debugreg.h>
#include <asm/siginfo.h> /* TRAP_TRACE, ... */
@@ -38,6 +40,7 @@
asmlinkage void machine_check(void);
#endif /* CONFIG_X86_MCE */
asmlinkage void simd_coprocessor_error(void);
+asmlinkage void emulate_vsyscall(void);
dotraplinkage void do_divide_error(struct pt_regs *, long);
dotraplinkage void do_debug(struct pt_regs *, long);
@@ -64,6 +67,7 @@
dotraplinkage void do_machine_check(struct pt_regs *, long);
#endif
dotraplinkage void do_simd_coprocessor_error(struct pt_regs *, long);
+dotraplinkage void do_emulate_vsyscall(struct pt_regs *, long);
#ifdef CONFIG_X86_32
dotraplinkage void do_iret_error(struct pt_regs *, long);
#endif
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index d555973..bb710cb 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -31,6 +31,18 @@
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 */