diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2014-05-14 16:33:54 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2014-05-14 16:33:54 -0700 |
| commit | fa81511bb0bbb2b1aace3695ce869da9762624ff (patch) | |
| tree | 4feff999a6217471bc23f997ef77bc492b225ffc /arch/x86/kernel/ldt.c | |
| parent | 9844f5462392b53824e8b86726e7c33b5ecbb676 (diff) | |
x86-64, modify_ldt: Make support for 16-bit segments a runtime option
Checkin:
b3b42ac2cbae x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels
disabled 16-bit segments on 64-bit kernels due to an information
leak. However, it does seem that people are genuinely using Wine to
run old 16-bit Windows programs on Linux.
A proper fix for this ("espfix64") is coming in the upcoming merge
window, but as a temporary fix, create a sysctl to allow the
administrator to re-enable support for 16-bit segments.
It adds a "/proc/sys/abi/ldt16" sysctl that defaults to zero (off). If
you hit this issue and care about your old Windows program more than
you care about a kernel stack address information leak, you can do
echo 1 > /proc/sys/abi/ldt16
as root (add it to your startup scripts), and you should be ok.
The sysctl table is only added if you have COMPAT support enabled on
x86-64, but I assume anybody who runs old windows binaries very much
does that ;)
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/CA%2B55aFw9BPoD10U1LfHbOMpHWZkvJTkMcfCs9s3urPr1YyWBxw@mail.gmail.com
Cc: <stable@vger.kernel.org>
Diffstat (limited to 'arch/x86/kernel/ldt.c')
| -rw-r--r-- | arch/x86/kernel/ldt.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index af1d14a9ebd..dcbbaa165bd 100644 --- a/arch/x86/kernel/ldt.c +++ b/arch/x86/kernel/ldt.c @@ -20,6 +20,8 @@ #include <asm/mmu_context.h> #include <asm/syscalls.h> +int sysctl_ldt16 = 0; + #ifdef CONFIG_SMP static void flush_ldt(void *current_mm) { @@ -234,7 +236,7 @@ static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) * IRET leaking the high bits of the kernel stack address. */ #ifdef CONFIG_X86_64 - if (!ldt_info.seg_32bit) { + if (!ldt_info.seg_32bit && !sysctl_ldt16) { error = -EINVAL; goto out_unlock; } |