Messages in this thread Patch in this message | | | From | Ben Hutchings <> | Date | Sat, 07 Jun 2014 02:26:29 +0100 | Subject | [PATCH 3.2 72/92] x86-64, modify_ldt: Make support for 16-bit segments a runtime option |
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3.2.60-rc1 review patch. If anyone has any objections, please let me know.
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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: Ben Hutchings <ben@decadent.org.uk> --- 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 @@ -21,6 +21,8 @@ #include <asm/mmu_context.h> #include <asm/syscalls.h> +int sysctl_ldt16 = 0; + #ifdef CONFIG_SMP static void flush_ldt(void *current_mm) { @@ -235,7 +237,7 @@ 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 /* @@ -387,6 +388,13 @@ 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 }, {} };
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