From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit fa81511bb0bbb2b1aace3695ce869da9762624ff upstream.
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@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/CA%2B55aFw9BPoD10U1LfHbOMpHWZkvJTkMcfCs9s3urPr1YyWBxw@xxxxxxxxxxxxxx
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
arch/x86/kernel/ldt.c | 4 +++-
arch/x86/vdso/vdso32-setup.c | 8 ++++++++
2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index af1d14a9ebda..dcbbaa165bde 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;
}
diff --git a/arch/x86/vdso/vdso32-setup.c b/arch/x86/vdso/vdso32-setup.c
index d6bfb876cfb0..f1d633a43f8e 100644
--- a/arch/x86/vdso/vdso32-setup.c
+++ b/arch/x86/vdso/vdso32-setup.c
@@ -41,6 +41,7 @@ enum {
#ifdef CONFIG_X86_64
#define vdso_enabled sysctl_vsyscall32
#define arch_setup_additional_pages syscall32_setup_pages
+extern int sysctl_ldt16;
#endif
/*
@@ -380,6 +381,13 @@ 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
+ },
{}
};
--
1.9.3
--
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