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Commit 1ad83c85 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Thomas Gleixner
Browse files

x86_64,vsyscall: Make vsyscall emulation configurable 



This adds CONFIG_X86_VSYSCALL_EMULATION, guarded by CONFIG_EXPERT.
Turning it off completely disables vsyscall emulation, saving ~3.5k
for vsyscall_64.c, 4k for vsyscall_emu_64.S (the fake vsyscall
page), some tiny amount of core mm code that supports a gate area,
and possibly 4k for a wasted pagetable.  The latter is because the
vsyscall addresses are misaligned and fit poorly in the fixmap.

Signed-off-by: default avatarAndy Lutomirski <luto@amacapital.net>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Link: http://lkml.kernel.org/r/406db88b8dd5f0cbbf38216d11be34bbb43c7eae.1414618407.git.luto@amacapital.net


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 95c46b56

arch/x86/Kconfig

+18 −0
Original line number Diff line number Diff line
@@ -984,6 +984,24 @@ config X86_ESPFIX64 
	def_bool y

	depends on X86_16BIT && X86_64



config X86_VSYSCALL_EMULATION

       bool "Enable vsyscall emulation" if EXPERT

       default y

       depends on X86_64

       ---help---

	 This enables emulation of the legacy vsyscall page.  Disabling

	 it is roughly equivalent to booting with vsyscall=none, except

	 that it will also disable the helpful warning if a program

	 tries to use a vsyscall.  With this option set to N, offending

	 programs will just segfault, citing addresses of the form

	 0xffffffffff600?00.



	 This option is required by many programs built before 2013, and

	 care should be used even with newer programs if set to N.



	 Disabling this option saves about 7K of kernel size and

	 possibly 4K of additional runtime pagetable memory.



config TOSHIBA

	tristate "Toshiba Laptop support"

	depends on X86_32

arch/x86/include/asm/fixmap.h

+2 −0
Original line number Diff line number Diff line
@@ -69,7 +69,9 @@ enum fixed_addresses { 
#ifdef CONFIG_X86_32

	FIX_HOLE,

#else

#ifdef CONFIG_X86_VSYSCALL_EMULATION

	VSYSCALL_PAGE = (FIXADDR_TOP - VSYSCALL_ADDR) >> PAGE_SHIFT,

#endif

#ifdef CONFIG_PARAVIRT_CLOCK

	PVCLOCK_FIXMAP_BEGIN,

	PVCLOCK_FIXMAP_END = PVCLOCK_FIXMAP_BEGIN+PVCLOCK_VSYSCALL_NR_PAGES-1,

arch/x86/include/asm/page_64.h

+3 −1
Original line number Diff line number Diff line
@@ -39,6 +39,8 @@ void copy_page(void *to, void *from); 


#endif	/* !__ASSEMBLY__ */



#ifdef CONFIG_X86_VSYSCALL_EMULATION

# define __HAVE_ARCH_GATE_AREA 1

#endif



#endif /* _ASM_X86_PAGE_64_H */

arch/x86/include/asm/vsyscall.h

+8 −0
Original line number Diff line number Diff line
@@ -4,6 +4,7 @@ 
#include <linux/seqlock.h>

#include <uapi/asm/vsyscall.h>



#ifdef CONFIG_X86_VSYSCALL_EMULATION

extern void map_vsyscall(void);



/*
@@ -11,5 +12,12 @@ extern void map_vsyscall(void); 
 * Returns true if handled.

 */

extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address);

#else

static inline void map_vsyscall(void) {}

static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address)

{

	return false;

}

#endif



#endif /* _ASM_X86_VSYSCALL_H */

arch/x86/kernel/Makefile

+1 −2
Original line number Diff line number Diff line
@@ -28,8 +28,7 @@ obj-$(CONFIG_X86_32) += i386_ksyms_32.o 
obj-$(CONFIG_X86_64)	+= sys_x86_64.o x8664_ksyms_64.o

obj-$(CONFIG_X86_64)	+= mcount_64.o

obj-y			+= syscall_$(BITS).o vsyscall_gtod.o

obj-$(CONFIG_X86_64)	+= vsyscall_64.o

obj-$(CONFIG_X86_64)	+= vsyscall_emu_64.o

obj-$(CONFIG_X86_VSYSCALL_EMULATION)	+= vsyscall_64.o vsyscall_emu_64.o

obj-$(CONFIG_X86_ESPFIX64)	+= espfix_64.o

obj-$(CONFIG_SYSFS)	+= ksysfs.o

obj-y			+= bootflag.o e820.o