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x86-64, modify_ldt: Make support for 16-bit segments a runtime option

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b3b42ac2cb 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>
This commit is contained in:
Linus Torvalds 2014-05-14 16:33:54 -07:00 committed by H. Peter Anvin
parent 9844f54623
commit fa81511bb0
2 changed files with 11 additions and 1 deletions
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4
arch/x86/kernel/ldt.c
View File

@ -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;
}

8
arch/x86/vdso/vdso32-setup.c
View File

@ -39,6 +39,7 @@
#ifdef CONFIG_X86_64
#define vdso_enabled sysctl_vsyscall32
#define arch_setup_additional_pages syscall32_setup_pages
extern int sysctl_ldt16;
#endif
/*
@ -249,6 +250,13 @@ static struct ctl_table abi_table2[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
{
.procname = "ldt16",
.data = &sysctl_ldt16,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec
},
{}
};