Commit 309944be authored Mar 17, 2014 by Andy Lutomirski Committed by H. Peter Anvin Mar 18, 2014

x86, vdso: Zero-pad the VVAR page



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>

parent 7c03156f

arch/x86/kernel/vmlinux.lds.S

+5 −0

Original line number	Diff line number	Diff line
		@@ -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);