Messages in this thread Patch in this message | | | From | Stefani Seibold <> | Subject | [PATCH v21 12/12] x86: Zero-pad the VVAR page | Date | Sun, 2 Mar 2014 10:20:20 +0100 |
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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: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Stefani Seibold <stefani@seibold.net> --- arch/x86/kernel/vmlinux.lds.S | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 1d4897b..49edf2d 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -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); -- 1.9.0
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