Re: [patch 1/2] Relocate VDSO ELF headers to match mapped locationwith COMPAT_VDSO

From: Jeremy Fitzhardinge
Date: Thu Apr 05 2007 - 04:19:29 EST

Roland McGrath wrote:
>> In addition to Roland's remarks about missing symbol table relocation, I
>> would also assume section headers, if present, should be relocated.
>>
>
> Yes, and also the .symtab as well as .dynsym just in case one ever has one
> (though I think they are built stripped now, it's not hard to check sh_type
> for SHT_SYMTAB and call the same routine that works from DT_SYMTAB).
>

OK, how does this look? Does it need to worry about DT_REL/DT_RELA
tags? (Not that there are any.)

J

Subject: Relocate VDSO ELF headers to match mapped location with COMPAT_VDSO

Some versions of libc can't deal with a VDSO which doesn't have its
ELF headers matching its mapped address. COMPAT_VDSO maps the VDSO at
a specific system-wide fixed address. Previously this was all done at
build time, on the grounds that the fixed VDSO address is always at
the top of the address space. However, a hypervisor may reserve some
of that address space, pushing the fixmap address down.

This patch does the adjustment dynamically at runtime, depending on
the runtime location of the VDSO fixmap.

[ Patch has been through several hands: Jan Beulich wrote the orignal
version; Zach reworked it, and Jeremy converted it to relocate phdrs
rather than sections. ]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Cc: Zachary Amsden <zach@xxxxxxxxxx>
Cc: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>

---
arch/i386/kernel/entry.S | 4 -
arch/i386/kernel/sysenter.c | 95 ++++++++++++++++++++++++++++++++++++-------
arch/i386/mm/pgtable.c | 6 --
include/asm-i386/elf.h | 28 ++++--------
include/asm-i386/fixmap.h | 8 ---
include/linux/elf.h | 3 +
6 files changed, 95 insertions(+), 49 deletions(-)

diff -r 97a792fb6127 arch/i386/kernel/entry.S
--- a/arch/i386/kernel/entry.S Wed Apr 04 23:26:37 2007 -0700
+++ b/arch/i386/kernel/entry.S Thu Apr 05 01:11:25 2007 -0700
@@ -305,16 +305,12 @@ sysenter_past_esp:
pushl $(__USER_CS)
CFI_ADJUST_CFA_OFFSET 4
/*CFI_REL_OFFSET cs, 0*/
-#ifndef CONFIG_COMPAT_VDSO
/*
* Push current_thread_info()->sysenter_return to the stack.
* A tiny bit of offset fixup is necessary - 4*4 means the 4 words
* pushed above; +8 corresponds to copy_thread's esp0 setting.
*/
pushl (TI_sysenter_return-THREAD_SIZE+8+4*4)(%esp)
-#else
- pushl $SYSENTER_RETURN
-#endif
CFI_ADJUST_CFA_OFFSET 4
CFI_REL_OFFSET eip, 0

diff -r 97a792fb6127 arch/i386/kernel/sysenter.c
--- a/arch/i386/kernel/sysenter.c Wed Apr 04 23:26:37 2007 -0700
+++ b/arch/i386/kernel/sysenter.c Thu Apr 05 01:11:25 2007 -0700
@@ -22,6 +22,7 @@
#include <asm/msr.h>
#include <asm/pgtable.h>
#include <asm/unistd.h>
+#include <asm/elf.h>

/*
* Should the kernel map a VDSO page into processes and pass its
@@ -41,6 +42,102 @@ __setup("vdso=", vdso_setup);
__setup("vdso=", vdso_setup);

extern asmlinkage void sysenter_entry(void);
+
+#ifdef CONFIG_COMPAT_VDSO
+static __cpuinit 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 */
+
+ switch(ELF_ST_TYPE(sym->st_info)) {
+ case STT_OBJECT:
+ case STT_FUNC:
+ case STT_SECTION:
+ case STT_FILE:
+ sym->st_value += VDSO_HIGH_BASE;
+ }
+ }
+}
+
+struct elfhash {
+ Elf32_Word nbucket, nchain;
+};
+
+static __cpuinit 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_ENCODING ... DT_HIOS:
+ /* tags above DT_ENCODING are even if they're
+ a pointer, so skip odd ones */
+ if (dyn->d_tag >= DT_ENCODING &&
+ (dyn->d_tag & 1) == 1)
+ break;
+
+ dyn->d_un.d_ptr += VDSO_HIGH_BASE;
+ }
+}
+
+static __cpuinit void relocate_vdso(Elf32_Ehdr *ehdr)
+{
+ Elf32_Phdr *phdr;
+ Elf32_Shdr *shdr;
+ int i;
+
+ BUG_ON(memcmp(ehdr->e_ident, ELFMAG, 4) != 0 ||
+ !elf_check_arch(ehdr) ||
+ ehdr->e_type != ET_DYN);
+
+ ehdr->e_entry += VDSO_HIGH_BASE;
+
+ /* rebase phdrs */
+ phdr = (void *)ehdr + ehdr->e_phoff;
+ for (i = 0; i < ehdr->e_phnum; i++) {
+ phdr[i].p_vaddr += VDSO_HIGH_BASE;
+
+ /* 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++) {
+ shdr[i].sh_addr += VDSO_HIGH_BASE;
+
+ if (shdr[i].sh_type == SHT_SYMTAB ||
+ shdr[i].sh_type == SHT_DYNSYM)
+ reloc_symtab(ehdr, shdr[i].sh_offset,
+ shdr[i].sh_size);
+ }
+}
+#else
+static inline void relocate_vdso(Elf32_Ehdr *ehdr)
+{
+}
+#endif /* COMPAT_VDSO */

void enable_sep_cpu(void)
{
@@ -71,6 +168,9 @@ int __cpuinit sysenter_setup(void)
int __cpuinit sysenter_setup(void)
{
void *syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
+ const void *vsyscall;
+ size_t vsyscall_len;
+
syscall_pages[0] = virt_to_page(syscall_page);

#ifdef CONFIG_COMPAT_VDSO
@@ -79,23 +179,23 @@ int __cpuinit sysenter_setup(void)
#endif

if (!boot_cpu_has(X86_FEATURE_SEP)) {
- memcpy(syscall_page,
- &vsyscall_int80_start,
- &vsyscall_int80_end - &vsyscall_int80_start);
- return 0;
- }
-
- memcpy(syscall_page,
- &vsyscall_sysenter_start,
- &vsyscall_sysenter_end - &vsyscall_sysenter_start);
-
- return 0;
-}
-
-#ifndef CONFIG_COMPAT_VDSO
+ vsyscall = &vsyscall_int80_start;
+ vsyscall_len = &vsyscall_int80_end - &vsyscall_int80_start;
+ } else {
+ vsyscall = &vsyscall_sysenter_start;
+ vsyscall_len = &vsyscall_sysenter_end - &vsyscall_sysenter_start;
+ }
+
+ memcpy(syscall_page, vsyscall, vsyscall_len);
+ relocate_vdso(syscall_page);
+
+ return 0;
+}
+
/* 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)
{
@@ -155,4 +255,17 @@ int in_gate_area_no_task(unsigned long a
{
return 0;
}
-#endif
+#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 -r 97a792fb6127 arch/i386/mm/pgtable.c
--- a/arch/i386/mm/pgtable.c Wed Apr 04 23:26:37 2007 -0700
+++ b/arch/i386/mm/pgtable.c Thu Apr 05 01:11:25 2007 -0700
@@ -144,10 +144,8 @@ void set_pmd_pfn(unsigned long vaddr, un
}

static int fixmaps;
-#ifndef CONFIG_COMPAT_VDSO
unsigned long __FIXADDR_TOP = 0xfffff000;
EXPORT_SYMBOL(__FIXADDR_TOP);
-#endif

void __set_fixmap (enum fixed_addresses idx, unsigned long phys, pgprot_t flags)
{
@@ -173,12 +171,8 @@ void reserve_top_address(unsigned long r
BUG_ON(fixmaps > 0);
printk(KERN_INFO "Reserving virtual address space above 0x%08x\n",
(int)-reserve);
-#ifdef CONFIG_COMPAT_VDSO
- BUG_ON(reserve != 0);
-#else
__FIXADDR_TOP = -reserve - PAGE_SIZE;
__VMALLOC_RESERVE += reserve;
-#endif
}

pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
diff -r 97a792fb6127 include/asm-i386/elf.h
--- a/include/asm-i386/elf.h Wed Apr 04 23:26:37 2007 -0700
+++ b/include/asm-i386/elf.h Thu Apr 05 01:11:25 2007 -0700
@@ -133,39 +133,31 @@ extern int dump_task_extended_fpu (struc
#define ELF_CORE_COPY_XFPREGS(tsk, elf_xfpregs) dump_task_extended_fpu(tsk, elf_xfpregs)

#define VDSO_HIGH_BASE (__fix_to_virt(FIX_VDSO))
-#define VDSO_BASE ((unsigned long)current->mm->context.vdso)
-
-#ifdef CONFIG_COMPAT_VDSO
-# define VDSO_COMPAT_BASE VDSO_HIGH_BASE
-# define VDSO_PRELINK VDSO_HIGH_BASE
-#else
-# define VDSO_COMPAT_BASE VDSO_BASE
-# define VDSO_PRELINK 0
-#endif
+#define VDSO_CURRENT_BASE ((unsigned long)current->mm->context.vdso)
+#define VDSO_PRELINK 0

#define VDSO_SYM(x) \
- (VDSO_COMPAT_BASE + (unsigned long)(x) - VDSO_PRELINK)
+ (VDSO_CURRENT_BASE + (unsigned long)(x) - VDSO_PRELINK)

#define VDSO_HIGH_EHDR ((const struct elfhdr *) VDSO_HIGH_BASE)
-#define VDSO_EHDR ((const struct elfhdr *) VDSO_COMPAT_BASE)
+#define VDSO_EHDR ((const struct elfhdr *) VDSO_CURRENT_BASE)

extern void __kernel_vsyscall;

#define VDSO_ENTRY VDSO_SYM(&__kernel_vsyscall)

-#ifndef CONFIG_COMPAT_VDSO
+struct linux_binprm;
+
#define ARCH_HAS_SETUP_ADDITIONAL_PAGES
-struct linux_binprm;
extern int arch_setup_additional_pages(struct linux_binprm *bprm,
int executable_stack);
-#endif

extern unsigned int vdso_enabled;

-#define ARCH_DLINFO \
-do if (vdso_enabled) { \
- NEW_AUX_ENT(AT_SYSINFO, VDSO_ENTRY); \
- NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_COMPAT_BASE); \
+#define ARCH_DLINFO \
+do if (vdso_enabled) { \
+ NEW_AUX_ENT(AT_SYSINFO, VDSO_ENTRY); \
+ NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_CURRENT_BASE); \
} while (0)

#endif
diff -r 97a792fb6127 include/asm-i386/fixmap.h
--- a/include/asm-i386/fixmap.h Wed Apr 04 23:26:37 2007 -0700
+++ b/include/asm-i386/fixmap.h Thu Apr 05 01:11:25 2007 -0700
@@ -19,13 +19,9 @@
* Leave one empty page between vmalloc'ed areas and
* the start of the fixmap.
*/
-#ifndef CONFIG_COMPAT_VDSO
extern unsigned long __FIXADDR_TOP;
-#else
-#define __FIXADDR_TOP 0xfffff000
-#define FIXADDR_USER_START __fix_to_virt(FIX_VDSO)
-#define FIXADDR_USER_END __fix_to_virt(FIX_VDSO - 1)
-#endif
+#define FIXADDR_USER_START __fix_to_virt(FIX_VDSO)
+#define FIXADDR_USER_END __fix_to_virt(FIX_VDSO - 1)

#ifndef __ASSEMBLY__
#include <linux/kernel.h>
diff -r 97a792fb6127 include/linux/elf.h
--- a/include/linux/elf.h Wed Apr 04 23:26:37 2007 -0700
+++ b/include/linux/elf.h Thu Apr 05 01:11:25 2007 -0700
@@ -83,6 +83,12 @@ typedef __s64 Elf64_Sxword;
#define DT_DEBUG 21
#define DT_TEXTREL 22
#define DT_JMPREL 23
+#define DT_ENCODING 32
+#define DT_LOOS 0x6000000D
+#define DT_HIOS 0x6ffff000
+#define DT_VERSYM 0x6ffffff0
+#define DT_VERDEF 0x6ffffffc
+#define DT_VERNEED 0x6ffffffe
#define DT_LOPROC 0x70000000
#define DT_HIPROC 0x7fffffff



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