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x86_64,vsyscall: Make vsyscall emulation configurable

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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: Andy Lutomirski <luto@amacapital.net>
Reviewed-by: Josh 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: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Andy Lutomirski 2014-10-29 14:33:47 -07:00 committed by Thomas Gleixner
parent 95c46b5692
commit 1ad83c858c
7 changed files with 36 additions and 7 deletions
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18
arch/x86/Kconfig
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@ -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

2
arch/x86/include/asm/fixmap.h
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@ -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,

4
arch/x86/include/asm/page_64.h
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@ -39,6 +39,8 @@ void copy_page(void *to, void *from);
#endif /* !__ASSEMBLY__ */
#define __HAVE_ARCH_GATE_AREA 1
#ifdef CONFIG_X86_VSYSCALL_EMULATION
# define __HAVE_ARCH_GATE_AREA 1
#endif
#endif /* _ASM_X86_PAGE_64_H */

8
arch/x86/include/asm/vsyscall.h
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@ -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 */

3
arch/x86/kernel/Makefile
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@ -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

2
arch/x86/kernel/setup.c
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@ -1190,9 +1190,7 @@ void __init setup_arch(char **cmdline_p)
tboot_probe();
#ifdef CONFIG_X86_64
map_vsyscall();
#endif
generic_apic_probe();

6
arch/x86/xen/mmu.c
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@ -1457,8 +1457,10 @@ static int xen_pgd_alloc(struct mm_struct *mm)
page->private = (unsigned long)user_pgd;
if (user_pgd != NULL) {
#ifdef CONFIG_X86_VSYSCALL_EMULATION
user_pgd[pgd_index(VSYSCALL_ADDR)] =
__pgd(__pa(level3_user_vsyscall) | _PAGE_TABLE);
#endif
ret = 0;
}
@ -2021,7 +2023,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
# ifdef CONFIG_HIGHMEM
case FIX_KMAP_BEGIN ... FIX_KMAP_END:
# endif
#else
#elif defined(CONFIG_X86_VSYSCALL_EMULATION)
case VSYSCALL_PAGE:
#endif
case FIX_TEXT_POKE0:
@ -2060,7 +2062,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
__native_set_fixmap(idx, pte);
#ifdef CONFIG_X86_64
#ifdef CONFIG_X86_VSYSCALL_EMULATION
/* Replicate changes to map the vsyscall page into the user
pagetable vsyscall mapping. */
if (idx == VSYSCALL_PAGE) {