[PATCH] i386: Make COMPAT_VDSO runtime selectable.

Now that relocation of the VDSO for COMPAT_VDSO users is done at
runtime rather than compile time, it is possible to enable/disable
compat mode at runtime.

This patch allows you to enable COMPAT_VDSO mode with "vdso=2" on the
kernel command line, or via sysctl.  (Switching on a running system
shouldn't be done lightly; any process which was relying on the compat
VDSO will be upset if it goes away.)

The COMPAT_VDSO config option still exists, but if enabled it just
makes vdso_enabled default to VDSO_COMPAT.

+From: Hugh Dickins <hugh@veritas.com>

Fix oops from i386-make-compat_vdso-runtime-selectable.patch.

Even mingetty at system startup finds it easy to trigger an oops
while reading /proc/PID/maps: though it has a good hold on the mm
itself, that cannot stop exit_mm() from resetting tsk->mm to NULL.

(It is usually show_map()'s call to get_gate_vma() which oopses,
and I expect we could change that to check priv->tail_vma instead;
but no matter, even m_start()'s call just after get_task_mm() is racy.)

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Zachary Amsden <zach@vmware.com>
Cc: "Jan Beulich" <JBeulich@novell.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Roland McGrath <roland@redhat.com>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 84c3bd0..4287696 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1820,6 +1820,7 @@ and is between 256 and 4096 characters. It is defined in the file
                        [USBHID] The interval which mice are to be polled at.
 
        vdso=           [IA-32,SH]
+                       vdso=2: enable compat VDSO (default with COMPAT_VDSO)
                        vdso=1: enable VDSO (default)
                        vdso=0: disable VDSO mapping
 

diff --git a/arch/i386/kernel/sysenter.c b/arch/i386/kernel/sysenter.c
index e5a9583..0b9768e 100644 (file)
--- a/arch/i386/kernel/sysenter.c
+++ b/arch/i386/kernel/sysenter.c
@@ -23,16 +23,25 @@
 #include <asm/pgtable.h>
 #include <asm/unistd.h>
 #include <asm/elf.h>
+#include <asm/tlbflush.h>
+
+enum {
+       VDSO_DISABLED = 0,
+       VDSO_ENABLED = 1,
+       VDSO_COMPAT = 2,
+};
+
+#ifdef CONFIG_COMPAT_VDSO
+#define VDSO_DEFAULT   VDSO_COMPAT
+#else
+#define VDSO_DEFAULT   VDSO_ENABLED
+#endif
 
 /*
  * Should the kernel map a VDSO page into processes and pass its
  * address down to glibc upon exec()?
  */
-#ifdef CONFIG_PARAVIRT
-unsigned int __read_mostly vdso_enabled = 0;
-#else
-unsigned int __read_mostly vdso_enabled = 1;
-#endif
+unsigned int __read_mostly vdso_enabled = VDSO_DEFAULT;
 
 EXPORT_SYMBOL_GPL(vdso_enabled);
 
@@ -47,7 +56,6 @@ __setup("vdso=", vdso_setup);
 
 extern asmlinkage void sysenter_entry(void);
 
-#ifdef CONFIG_COMPAT_VDSO
 static __init void reloc_symtab(Elf32_Ehdr *ehdr,
                                unsigned offset, unsigned size)
 {
@@ -164,11 +172,6 @@ static __init void relocate_vdso(Elf32_Ehdr *ehdr)
                                     shdr[i].sh_size);
        }
 }
-#else
-static inline void relocate_vdso(Elf32_Ehdr *ehdr)
-{
-}
-#endif /* COMPAT_VDSO */
 
 void enable_sep_cpu(void)
 {
@@ -188,6 +191,25 @@ void enable_sep_cpu(void)
        put_cpu();      
 }
 
+static struct vm_area_struct gate_vma;
+
+static int __init gate_vma_init(void)
+{
+       gate_vma.vm_mm = NULL;
+       gate_vma.vm_start = FIXADDR_USER_START;
+       gate_vma.vm_end = FIXADDR_USER_END;
+       gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;
+       gate_vma.vm_page_prot = __P101;
+       /*
+        * Make sure the vDSO gets into every core dump.
+        * Dumping its contents makes post-mortem fully interpretable later
+        * without matching up the same kernel and hardware config to see
+        * what PC values meant.
+        */
+       gate_vma.vm_flags |= VM_ALWAYSDUMP;
+       return 0;
+}
+
 /*
  * These symbols are defined by vsyscall.o to mark the bounds
  * of the ELF DSO images included therein.
@@ -196,6 +218,22 @@ extern const char vsyscall_int80_start, vsyscall_int80_end;
 extern const char vsyscall_sysenter_start, vsyscall_sysenter_end;
 static struct page *syscall_pages[1];
 
+static void map_compat_vdso(int map)
+{
+       static int vdso_mapped;
+
+       if (map == vdso_mapped)
+               return;
+
+       vdso_mapped = map;
+
+       __set_fixmap(FIX_VDSO, page_to_pfn(syscall_pages[0]) << PAGE_SHIFT,
+                    map ? PAGE_READONLY_EXEC : PAGE_NONE);
+
+       /* flush stray tlbs */
+       flush_tlb_all();
+}
+
 int __init sysenter_setup(void)
 {
        void *syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
@@ -204,10 +242,9 @@ int __init sysenter_setup(void)
 
        syscall_pages[0] = virt_to_page(syscall_page);
 
-#ifdef CONFIG_COMPAT_VDSO
-       __set_fixmap(FIX_VDSO, __pa(syscall_page), PAGE_READONLY_EXEC);
+       gate_vma_init();
+
        printk("Compat vDSO mapped to %08lx.\n", __fix_to_virt(FIX_VDSO));
-#endif
 
        if (!boot_cpu_has(X86_FEATURE_SEP)) {
                vsyscall = &vsyscall_int80_start;
@@ -226,42 +263,57 @@ int __init sysenter_setup(void)
 /* Defined in vsyscall-sysenter.S */
 extern void SYSENTER_RETURN;
 
-#ifdef __HAVE_ARCH_GATE_AREA
 /* Setup a VMA at program startup for the vsyscall page */
 int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
 {
        struct mm_struct *mm = current->mm;
        unsigned long addr;
        int ret;
+       bool compat;
 
        down_write(&mm->mmap_sem);
-       addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
-       if (IS_ERR_VALUE(addr)) {
-               ret = addr;
-               goto up_fail;
-       }
 
-       /*
-        * MAYWRITE to allow gdb to COW and set breakpoints
-        *
-        * Make sure the vDSO gets into every core dump.
-        * Dumping its contents makes post-mortem fully interpretable later
-        * without matching up the same kernel and hardware config to see
-        * what PC values meant.
-        */
-       ret = install_special_mapping(mm, addr, PAGE_SIZE,
-                                     VM_READ|VM_EXEC|
-                                     VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-                                     VM_ALWAYSDUMP,
-                                     syscall_pages);
-       if (ret)
-               goto up_fail;
+       /* Test compat mode once here, in case someone
+          changes it via sysctl */
+       compat = (vdso_enabled == VDSO_COMPAT);
+
+       map_compat_vdso(compat);
+
+       if (compat)
+               addr = VDSO_HIGH_BASE;
+       else {
+               addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
+               if (IS_ERR_VALUE(addr)) {
+                       ret = addr;
+                       goto up_fail;
+               }
+
+               /*
+                * MAYWRITE to allow gdb to COW and set breakpoints
+                *
+                * Make sure the vDSO gets into every core dump.
+                * Dumping its contents makes post-mortem fully
+                * interpretable later without matching up the same
+                * kernel and hardware config to see what PC values
+                * meant.
+                */
+               ret = install_special_mapping(mm, addr, PAGE_SIZE,
+                                             VM_READ|VM_EXEC|
+                                             VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
+                                             VM_ALWAYSDUMP,
+                                             syscall_pages);
+
+               if (ret)
+                       goto up_fail;
+       }
 
        current->mm->context.vdso = (void *)addr;
        current_thread_info()->sysenter_return =
-                                   (void *)VDSO_SYM(&SYSENTER_RETURN);
-up_fail:
+               (void *)VDSO_SYM(&SYSENTER_RETURN);
+
+  up_fail:
        up_write(&mm->mmap_sem);
+
        return ret;
 }
 
@@ -274,6 +326,11 @@ const char *arch_vma_name(struct vm_area_struct *vma)
 
 struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
 {
+       struct mm_struct *mm = tsk->mm;
+
+       /* Check to see if this task was created in compat vdso mode */
+       if (mm && mm->context.vdso == (void *)VDSO_HIGH_BASE)
+               return &gate_vma;
        return NULL;
 }
 
@@ -286,17 +343,3 @@ int in_gate_area_no_task(unsigned long addr)
 {
        return 0;
 }
-#else  /* !__HAVE_ARCH_GATE_AREA */
-int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
-{
-       /*
-        * If not creating userspace VMA, simply set vdso to point to
-        * fixmap page.
-        */
-       current->mm->context.vdso = (void *)VDSO_HIGH_BASE;
-       current_thread_info()->sysenter_return =
-               (void *)VDSO_SYM(&SYSENTER_RETURN);
-
-       return 0;
-}
-#endif /* __HAVE_ARCH_GATE_AREA */

diff --git a/include/asm-i386/page.h b/include/asm-i386/page.h
index 7b19f45..fd3f64a 100644 (file)
--- a/include/asm-i386/page.h
+++ b/include/asm-i386/page.h
@@ -143,9 +143,7 @@ extern int page_is_ram(unsigned long pagenr);
 #include <asm-generic/memory_model.h>
 #include <asm-generic/page.h>
 
-#ifndef CONFIG_COMPAT_VDSO
 #define __HAVE_ARCH_GATE_AREA 1
-#endif
 #endif /* __KERNEL__ */
 
 #endif /* _I386_PAGE_H */