x86, vdso: Remove compat vdso support

The compat vDSO is a complicated hack that's needed to maintain
compatibility with a small range of glibc versions.

This removes it and replaces it with a much simpler hack: a config
option to disable the 32-bit vDSO by default.

This also changes the default value of CONFIG_COMPAT_VDSO to n --
users configuring kernels from scratch almost certainly want that
choice.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/4bb4690899106eb11430b1186d5cc66ca9d1660c.1394751608.git.luto@amacapital.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 21 insertions, 211 deletions

diff --git a/arch/x86/vdso/vdso32-setup.c b/arch/x86/vdso/vdso32-setup.c
index d6bfb876cfb0..ab20c04b688a 100644
--- a/arch/x86/vdso/vdso32-setup.c
+++ b/arch/x86/vdso/vdso32-setup.c
@@ -26,16 +26,10 @@
 #include <asm/vdso.h>
 #include <asm/proto.h>
 
-enum {
-        VDSO_DISABLED = 0,
-        VDSO_ENABLED = 1,
-        VDSO_COMPAT = 2,
-};
-
 #ifdef CONFIG_COMPAT_VDSO
-#define VDSO_DEFAULT    VDSO_COMPAT
+#define VDSO_DEFAULT    0
 #else
-#define VDSO_DEFAULT    VDSO_ENABLED
+#define VDSO_DEFAULT    1
 #endif
 
 #ifdef CONFIG_X86_64
@@ -44,13 +38,6 @@ enum {
 #endif
 
 /*
- * This is the difference between the prelinked addresses in the vDSO images
- * and the VDSO_HIGH_BASE address where CONFIG_COMPAT_VDSO places the vDSO
- * in the user address space.
- */
-#define VDSO_ADDR_ADJUST        (VDSO_HIGH_BASE - (unsigned long)VDSO32_PRELINK)
-
-/*
  * Should the kernel map a VDSO page into processes and pass its
  * address down to glibc upon exec()?
  */
@@ -60,6 +47,9 @@ static int __init vdso_setup(char *s)
 {
         vdso_enabled = simple_strtoul(s, NULL, 0);
 
+        if (vdso_enabled > 1)
+                pr_warn("vdso32 values other than 0 and 1 are no longer allowed; vdso disabled\n");
+
         return 1;
 }
 
@@ -76,123 +66,6 @@ __setup_param("vdso=", vdso32_setup, vdso_setup, 0);
 EXPORT_SYMBOL_GPL(vdso_enabled);
 #endif
 
-static __init void reloc_symtab(Elf32_Ehdr *ehdr,
-                                unsigned offset, unsigned size)
-{
-        Elf32_Sym *sym = (void *)ehdr + offset;
-        unsigned nsym = size / sizeof(*sym);
-        unsigned i;
-
-        for(i = 0; i < nsym; i++, sym++) {
-                if (sym->st_shndx == SHN_UNDEF ||
-                    sym->st_shndx == SHN_ABS)
-                        continue;  /* skip */
-
-                if (sym->st_shndx > SHN_LORESERVE) {
-                        printk(KERN_INFO "VDSO: unexpected st_shndx %x\n",
-                               sym->st_shndx);
-                        continue;
-                }
-
-                switch(ELF_ST_TYPE(sym->st_info)) {
-                case STT_OBJECT:
-                case STT_FUNC:
-                case STT_SECTION:
-                case STT_FILE:
-                        sym->st_value += VDSO_ADDR_ADJUST;
-                }
-        }
-}
-
-static __init void reloc_dyn(Elf32_Ehdr *ehdr, unsigned offset)
-{
-        Elf32_Dyn *dyn = (void *)ehdr + offset;
-
-        for(; dyn->d_tag != DT_NULL; dyn++)
-                switch(dyn->d_tag) {
-                case DT_PLTGOT:
-                case DT_HASH:
-                case DT_STRTAB:
-                case DT_SYMTAB:
-                case DT_RELA:
-                case DT_INIT:
-                case DT_FINI:
-                case DT_REL:
-                case DT_DEBUG:
-                case DT_JMPREL:
-                case DT_VERSYM:
-                case DT_VERDEF:
-                case DT_VERNEED:
-                case DT_ADDRRNGLO ... DT_ADDRRNGHI:
-                        /* definitely pointers needing relocation */
-                        dyn->d_un.d_ptr += VDSO_ADDR_ADJUST;
-                        break;
-
-                case DT_ENCODING ... OLD_DT_LOOS-1:
-                case DT_LOOS ... DT_HIOS-1:
-                        /* Tags above DT_ENCODING are pointers if
-                           they're even */
-                        if (dyn->d_tag >= DT_ENCODING &&
-                            (dyn->d_tag & 1) == 0)
-                                dyn->d_un.d_ptr += VDSO_ADDR_ADJUST;
-                        break;
-
-                case DT_VERDEFNUM:
-                case DT_VERNEEDNUM:
-                case DT_FLAGS_1:
-                case DT_RELACOUNT:
-                case DT_RELCOUNT:
-                case DT_VALRNGLO ... DT_VALRNGHI:
-                        /* definitely not pointers */
-                        break;
-
-                case OLD_DT_LOOS ... DT_LOOS-1:
-                case DT_HIOS ... DT_VALRNGLO-1:
-                default:
-                        if (dyn->d_tag > DT_ENCODING)
-                                printk(KERN_INFO "VDSO: unexpected DT_tag %x\n",
-                                       dyn->d_tag);
-                        break;
-                }
-}
-
-static __init void relocate_vdso(Elf32_Ehdr *ehdr)
-{
-        Elf32_Phdr *phdr;
-        Elf32_Shdr *shdr;
-        int i;
-
-        BUG_ON(memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0 ||
-               !elf_check_arch_ia32(ehdr) ||
-               ehdr->e_type != ET_DYN);
-
-        ehdr->e_entry += VDSO_ADDR_ADJUST;
-
-        /* rebase phdrs */
-        phdr = (void *)ehdr + ehdr->e_phoff;
-        for (i = 0; i < ehdr->e_phnum; i++) {
-                phdr[i].p_vaddr += VDSO_ADDR_ADJUST;
-
-                /* relocate dynamic stuff */
-                if (phdr[i].p_type == PT_DYNAMIC)
-                        reloc_dyn(ehdr, phdr[i].p_offset);
-        }
-
-        /* rebase sections */
-        shdr = (void *)ehdr + ehdr->e_shoff;
-        for(i = 0; i < ehdr->e_shnum; i++) {
-                if (!(shdr[i].sh_flags & SHF_ALLOC))
-                        continue;
-
-                shdr[i].sh_addr += VDSO_ADDR_ADJUST;
-
-                if (shdr[i].sh_type == SHT_SYMTAB ||
-                    shdr[i].sh_type == SHT_DYNSYM)
-                        reloc_symtab(ehdr, shdr[i].sh_offset,
-                                     shdr[i].sh_size);
-        }
-}
-
 static struct page *vdso32_pages[1];
 
 #ifdef CONFIG_X86_64
@@ -212,12 +85,6 @@ void syscall32_cpu_init(void)
         wrmsrl(MSR_CSTAR, ia32_cstar_target);
 }
 
-#define compat_uses_vma         1
-
-static inline void map_compat_vdso(int map)
-{
-}
-
 #else  /* CONFIG_X86_32 */
 
 #define vdso32_sysenter()       (boot_cpu_has(X86_FEATURE_SEP))
@@ -241,37 +108,6 @@ 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;
-
-        return 0;
-}
-
-#define compat_uses_vma         0
-
-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(vdso32_pages[0]) << PAGE_SHIFT,
-                     map ? PAGE_READONLY_EXEC : PAGE_NONE);
-
-        /* flush stray tlbs */
-        flush_tlb_all();
-}
-
 #endif  /* CONFIG_X86_64 */
 
 int __init sysenter_setup(void)
@@ -282,10 +118,6 @@ int __init sysenter_setup(void)
 
         vdso32_pages[0] = virt_to_page(syscall_page);
 
-#ifdef CONFIG_X86_32
-        gate_vma_init();
-#endif
-
         if (vdso32_syscall()) {
                 vsyscall = &vdso32_syscall_start;
                 vsyscall_len = &vdso32_syscall_end - &vdso32_syscall_start;
@@ -298,7 +130,6 @@ int __init sysenter_setup(void)
         }
 
         memcpy(syscall_page, vsyscall, vsyscall_len);
-        relocate_vdso(syscall_page);
 
         return 0;
 }
@@ -309,48 +140,35 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
         struct mm_struct *mm = current->mm;
         unsigned long addr;
         int ret = 0;
-        bool compat;
 
 #ifdef CONFIG_X86_X32_ABI
         if (test_thread_flag(TIF_X32))
                 return x32_setup_additional_pages(bprm, uses_interp);
 #endif
 
-        if (vdso_enabled == VDSO_DISABLED)
+        if (vdso_enabled != 1)  /* Other values all mean "disabled" */
                 return 0;
 
         down_write(&mm->mmap_sem);
 
-        /* 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;
-                }
+        addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
+        if (IS_ERR_VALUE(addr)) {
+                ret = addr;
+                goto up_fail;
         }
 
         current->mm->context.vdso = (void *)addr;
 
-        if (compat_uses_vma || !compat) {
-                /*
-                 * MAYWRITE to allow gdb to COW and set breakpoints
-                 */
-                ret = install_special_mapping(mm, addr, PAGE_SIZE,
-                                              VM_READ|VM_EXEC|
-                                              VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
-                                              vdso32_pages);
-
-                if (ret)
-                        goto up_fail;
-        }
+        /*
+         * MAYWRITE to allow gdb to COW and set breakpoints
+         */
+        ret = install_special_mapping(mm, addr, PAGE_SIZE,
+                                      VM_READ|VM_EXEC|
+                                      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
+                                      vdso32_pages);
+
+        if (ret)
+                goto up_fail;
 
         current_thread_info()->sysenter_return =
                 VDSO32_SYMBOL(addr, SYSENTER_RETURN);
@@ -411,20 +229,12 @@ const char *arch_vma_name(struct vm_area_struct *vma)
 
 struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
 {
-        /*
-         * Check to see if the corresponding task was created in compat vdso
-         * mode.
-         */
-        if (mm && mm->context.vdso == (void *)VDSO_HIGH_BASE)
-                return &gate_vma;
         return NULL;
 }
 
 int in_gate_area(struct mm_struct *mm, unsigned long addr)
 {
-        const struct vm_area_struct *vma = get_gate_vma(mm);
-
-        return vma && addr >= vma->vm_start && addr < vma->vm_end;
+        return 0;
 }
 
 int in_gate_area_no_mm(unsigned long addr)