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

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Message-ID: <tip-57f90c3dfc75da89358735c06bf9bc9815b4183e@git.kernel.org>
Date:	Tue, 19 Jul 2016 00:33:03 -0700
From:	tip-bot for Andy Lutomirski <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, luto@...nel.org, tglx@...utronix.de,
	peterz@...radead.org, mingo@...nel.org, brgerst@...il.com,
	bp@...en8.de, hpa@...or.com, torvalds@...ux-foundation.org,
	dvlasenk@...hat.com, jpoimboe@...hat.com
Subject: [tip:x86/asm] x86/vdso: Error out if the vDSO isn't a valid DSO

Commit-ID:  57f90c3dfc75da89358735c06bf9bc9815b4183e
Gitweb:     http://git.kernel.org/tip/57f90c3dfc75da89358735c06bf9bc9815b4183e
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Mon, 18 Jul 2016 14:46:35 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
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@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/8a30e0a07c3b47ff917a8daa2df5e407cc0c6698.1468878336.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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++) {