[tip:x86/asm] x86/vdso: Error out if the vDSO isn't a valid DSO

From: tip-bot for Andy Lutomirski
Date: Tue Jul 19 2016 - 03:34:01 EST

Commit-ID: 57f90c3dfc75da89358735c06bf9bc9815b4183e
Gitweb: http://git.kernel.org/tip/57f90c3dfc75da89358735c06bf9bc9815b4183e
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Mon, 18 Jul 2016 14:46:35 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 19 Jul 2016 08:50:24 +0200

x86/vdso: Error out if the vDSO isn't a valid DSO

Some distros has been playing with toolchain changes that can affect
the type of ELF objects built. Occasionally, this goes wrong and
the vDSO ends up not being a DSO at all. This causes the kernel to
end up broken in a surprisingly subtle way -- glibc apparently
silently ignores a vDSO that isn't a DSO, so everything works,
albeit slowly, until users try a different libc implementation.

Make the kernel build process a bit more robust: fail outright if
the vDSO isn't ET_DYN or is missing its PT_DYNAMIC segment. I've
never seen this in an unmodified kernel.

See: https://github.com/docker/docker/issues/23378

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/8a30e0a07c3b47ff917a8daa2df5e407cc0c6698.1468878336.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
arch/x86/entry/vdso/vdso2c.h | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/entry/vdso/vdso2c.h b/arch/x86/entry/vdso/vdso2c.h
index 63a03bb..4f74119 100644
--- a/arch/x86/entry/vdso/vdso2c.h
+++ b/arch/x86/entry/vdso/vdso2c.h
@@ -22,6 +22,9 @@ static void BITSFUNC(go)(void *raw_addr, size_t raw_len,

ELF(Phdr) *pt = (ELF(Phdr) *)(raw_addr + GET_LE(&hdr->e_phoff));

+ if (hdr->e_type != ET_DYN)
+ fail("input is not a shared object\n");
/* Walk the segment table. */
for (i = 0; i < GET_LE(&hdr->e_phnum); i++) {
if (GET_LE(&pt[i].p_type) == PT_LOAD) {
@@ -49,6 +52,9 @@ static void BITSFUNC(go)(void *raw_addr, size_t raw_len,
if (stripped_len < load_size)
fail("stripped input is too short\n");

+ if (!dyn)
+ fail("input has no PT_DYNAMIC section -- your toolchain is buggy\n");
/* Walk the dynamic table */
for (i = 0; dyn + i < dyn_end &&
GET_LE(&dyn[i].d_tag) != DT_NULL; i++) {