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>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0af5250d..9122f6b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1836,17 +1836,29 @@
If unsure, say N.
config COMPAT_VDSO
- def_bool y
- prompt "Compat VDSO support"
+ def_bool n
+ prompt "Disable the 32-bit vDSO (needed for glibc 2.3.3)"
depends on X86_32 || IA32_EMULATION
---help---
- Map the 32-bit VDSO to the predictable old-style address too.
+ Certain buggy versions of glibc will crash if they are
+ presented with a 32-bit vDSO that is not mapped at the address
+ indicated in its segment table.
- Say N here if you are running a sufficiently recent glibc
- version (2.3.3 or later), to remove the high-mapped
- VDSO mapping and to exclusively use the randomized VDSO.
+ The bug was introduced by f866314b89d56845f55e6f365e18b31ec978ec3a
+ and fixed by 3b3ddb4f7db98ec9e912ccdf54d35df4aa30e04a and
+ 49ad572a70b8aeb91e57483a11dd1b77e31c4468. Glibc 2.3.3 is
+ the only released version with the bug, but OpenSUSE 9
+ contains a buggy "glibc 2.3.2".
- If unsure, say Y.
+ The symptom of the bug is that everything crashes on startup, saying:
+ dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
+
+ Saying Y here changes the default value of the vdso32 boot
+ option from 1 to 0, which turns off the 32-bit vDSO entirely.
+ This works around the glibc bug but hurts performance.
+
+ If unsure, say N: if you are compiling your own kernel, you
+ are unlikely to be using a buggy version of glibc.
config CMDLINE_BOOL
bool "Built-in kernel command line"
