[PATCH 3/3] x86_64,vsyscall: Make vsyscall emulation configurable
From: Andy Lutomirski
Date: Tue Oct 28 2014 - 13:22:53 EST
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@xxxxxxxxxxxxxx>
---
arch/x86/Kconfig | 18 ++++++++++++++++++
arch/x86/include/asm/fixmap.h | 2 ++
arch/x86/include/asm/page_64.h | 4 +++-
arch/x86/include/asm/vsyscall.h | 8 ++++++++
arch/x86/kernel/Makefile | 3 +--
arch/x86/kernel/setup.c | 2 --
arch/x86/xen/mmu.c | 6 ++++--
7 files changed, 36 insertions(+), 7 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f2327e88e07c..cd10436d7d1c 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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
diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index ffb1733ac91f..d8d5bcb2a0b5 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -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,
diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index f408caf73430..b3bebf9e5746 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -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 */
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index 34f7d8857542..6ba66ee79710 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -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 */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 8f1e77440b2b..5d4502c8b983 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -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
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 235cfd39e0d7..59a6f884fdad 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1190,9 +1190,7 @@ void __init setup_arch(char **cmdline_p)
tboot_probe();
-#ifdef CONFIG_X86_64
map_vsyscall();
-#endif
generic_apic_probe();
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index a8a1a3d08d4d..5046b699eec1 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1456,11 +1456,13 @@ static int xen_pgd_alloc(struct mm_struct *mm)
user_pgd = (pgd_t *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
page->private = (unsigned long)user_pgd;
+#ifdef CONFIG_X86_VSYSCALL_EMULATION
if (user_pgd != NULL) {
user_pgd[pgd_index(VSYSCALL_ADDR)] =
__pgd(__pa(level3_user_vsyscall) | _PAGE_TABLE);
ret = 0;
}
+#endif
BUG_ON(PagePinned(virt_to_page(xen_get_user_pgd(pgd))));
}
@@ -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) {
--
1.9.3
--
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