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: 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>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f2327e8..cd10436 100644 (file)
--- 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 ffb1733..d8d5bcb 100644 (file)
--- 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 f408caf..b3bebf9 100644 (file)
--- 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 34f7d88..6ba66ee 100644 (file)
--- 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 8f1e774..5d4502c 100644 (file)
--- 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 235cfd3..59a6f88 100644 (file)
--- 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 a8a1a3d..8906cf0 100644 (file)
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -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) {