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authorLinus Torvalds <torvalds@linux-foundation.org>2014-05-14 16:33:54 -0700
committerH. Peter Anvin <hpa@linux.intel.com>2014-05-14 16:33:54 -0700
commitfa81511bb0bbb2b1aace3695ce869da9762624ff (patch)
tree4feff999a6217471bc23f997ef77bc492b225ffc
parent9844f5462392b53824e8b86726e7c33b5ecbb676 (diff)
downloadblackbird-op-linux-fa81511bb0bbb2b1aace3695ce869da9762624ff.tar.gz
blackbird-op-linux-fa81511bb0bbb2b1aace3695ce869da9762624ff.zip
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>
-rw-r--r--arch/x86/kernel/ldt.c4
-rw-r--r--arch/x86/vdso/vdso32-setup.c8
2 files changed, 11 insertions, 1 deletions
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 00348980a3a6..e1f220e3ca68 100644
--- a/arch/x86/vdso/vdso32-setup.c
+++ b/arch/x86/vdso/vdso32-setup.c
@@ -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
+ },
{}
};
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