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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2014-05-14 16:33:54 -0700 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2014-06-09 13:29:12 +0100 |
| commit | 434ffe9cc9c9336f375f1acfb00993ee6f18bd80 (patch) | |
| tree | 3d4f8306933ad0a47982e7f509f84ac4accd625c /arch | |
| parent | 5b8d65ccb6e96f5fa066c018d9ef365fd3c8da9b (diff) | |
| download | lwn-434ffe9cc9c9336f375f1acfb00993ee6f18bd80.tar.gz lwn-434ffe9cc9c9336f375f1acfb00993ee6f18bd80.zip | |
x86-64, modify_ldt: Make support for 16-bit segments a runtime option
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>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kernel/ldt.c | 4 | ||||
| -rw-r--r-- | arch/x86/vdso/vdso32-setup.c | 8 |
2 files changed, 11 insertions, 1 deletions
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c index 4ac453114d7e..3e0ccbffff6b 100644 --- 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, 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 468d591dde31..51bdc0546733 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 /* @@ -388,6 +389,13 @@ static ctl_table abi_table2[] = { .mode = 0644, .proc_handler = proc_dointvec }, + { + .procname = "ldt16", + .data = &sysctl_ldt16, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec + }, {} }; |