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3fb2f4237b
It turns out that there's a lurking ABI issue. GCC, when
compiling this in a 32-bit program:
struct user_desc desc = {
.entry_number = idx,
.base_addr = base,
.limit = 0xfffff,
.seg_32bit = 1,
.contents = 0, /* Data, grow-up */
.read_exec_only = 0,
.limit_in_pages = 1,
.seg_not_present = 0,
.useable = 0,
};
will leave .lm uninitialized. This means that anything in the
kernel that reads user_desc.lm for 32-bit tasks is unreliable.
Revert the .lm check in set_thread_area(). The value never did
anything in the first place.
Fixes: 0e58af4e1d ("x86/tls: Disallow unusual TLS segments")
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org # Only if 0e58af4e1d is backported
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/d7875b60e28c512f6a6fc0baf5714d58e7eaadbb.1418856405.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
48 lines
1.2 KiB
C
48 lines
1.2 KiB
C
/*
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* ldt.h
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*
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* Definitions of structures used with the modify_ldt system call.
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*/
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#ifndef _ASM_X86_LDT_H
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#define _ASM_X86_LDT_H
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/* Maximum number of LDT entries supported. */
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#define LDT_ENTRIES 8192
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/* The size of each LDT entry. */
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#define LDT_ENTRY_SIZE 8
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#ifndef __ASSEMBLY__
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/*
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* Note on 64bit base and limit is ignored and you cannot set DS/ES/CS
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* not to the default values if you still want to do syscalls. This
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* call is more for 32bit mode therefore.
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*/
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struct user_desc {
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unsigned int entry_number;
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unsigned int base_addr;
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unsigned int limit;
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unsigned int seg_32bit:1;
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unsigned int contents:2;
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unsigned int read_exec_only:1;
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unsigned int limit_in_pages:1;
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unsigned int seg_not_present:1;
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unsigned int useable:1;
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#ifdef __x86_64__
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/*
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* Because this bit is not present in 32-bit user code, user
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* programs can pass uninitialized values here. Therefore, in
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* any context in which a user_desc comes from a 32-bit program,
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* the kernel must act as though lm == 0, regardless of the
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* actual value.
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*/
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unsigned int lm:1;
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#endif
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};
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#define MODIFY_LDT_CONTENTS_DATA 0
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#define MODIFY_LDT_CONTENTS_STACK 1
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#define MODIFY_LDT_CONTENTS_CODE 2
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#endif /* !__ASSEMBLY__ */
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#endif /* _ASM_X86_LDT_H */
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