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x86, vdso: Zero-pad the VVAR page

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By coincidence, the VVAR page is at the end of an ELF segment.  As a
result, if it ends up being a partial page, the kernel loader will
leave garbage behind at the end of the vvar page.  Zero-pad it to a
full page to fix this issue.

This has probably been broken since the VVAR page was introduced.
On QEMU, if you dump the run-time contents of the VVAR page, you can
find entertaining strings from seabios left behind.

It's remotely possible that this is a security bug -- conceivably
there's some BIOS out there that leaves something sensitive in the
few K of memory that is exposed to userspace.

Signed-off-by: Stefani Seibold <stefani@seibold.net>
Link: http://lkml.kernel.org/r/1395094933-14252-12-git-send-email-stefani@seibold.net
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Andy Lutomirski 2014-03-17 23:22:11 +01:00 committed by H. Peter Anvin
parent 7c03156f34
commit 309944be29
1 changed files with 5 additions and 0 deletions
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5
arch/x86/kernel/vmlinux.lds.S
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@ -164,6 +164,11 @@ SECTIONS
#undef __VVAR_KERNEL_LDS
#undef EMIT_VVAR
/*
* Pad the rest of the page with zeros. Otherwise the loader
* can leave garbage here.
*/
. = __vvar_beginning_hack + PAGE_SIZE;
} :data
. = ALIGN(__vvar_page + PAGE_SIZE, PAGE_SIZE);