| From fa81511bb0bbb2b1aace3695ce869da9762624ff Mon Sep 17 00:00:00 2001 |
| From: Linus Torvalds <torvalds@linux-foundation.org> |
| Date: Wed, 14 May 2014 16:33:54 -0700 |
| Subject: x86-64, modify_ldt: Make support for 16-bit segments a runtime option |
| |
| From: Linus Torvalds <torvalds@linux-foundation.org> |
| |
| 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@linux.intel.com> |
| Link: http://lkml.kernel.org/r/CA%2B55aFw9BPoD10U1LfHbOMpHWZkvJTkMcfCs9s3urPr1YyWBxw@mail.gmail.com |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/x86/kernel/ldt.c | 4 +++- |
| arch/x86/vdso/vdso32-setup.c | 8 ++++++++ |
| 2 files changed, 11 insertions(+), 1 deletion(-) |
| |
| --- 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, u |
| * 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; |
| } |
| --- 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 |
| |
| /* |
| @@ -379,6 +380,13 @@ static ctl_table abi_table2[] = { |
| .maxlen = sizeof(int), |
| .mode = 0644, |
| .proc_handler = proc_dointvec |
| + }, |
| + { |
| + .procname = "ldt16", |
| + .data = &sysctl_ldt16, |
| + .maxlen = sizeof(int), |
| + .mode = 0644, |
| + .proc_handler = proc_dointvec |
| }, |
| {} |
| }; |