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>
47 lines
1.2 KiB
C
47 lines
1.2 KiB
C
/*
|
|
* ldt.h
|
|
*
|
|
* Definitions of structures used with the modify_ldt system call.
|
|
*/
|
|
#ifndef _ASM_X86_LDT_H
|
|
#define _ASM_X86_LDT_H
|
|
|
|
/* Maximum number of LDT entries supported. */
|
|
#define LDT_ENTRIES 8192
|
|
/* The size of each LDT entry. */
|
|
#define LDT_ENTRY_SIZE 8
|
|
|
|
#ifndef __ASSEMBLY__
|
|
/*
|
|
* Note on 64bit base and limit is ignored and you cannot set DS/ES/CS
|
|
* not to the default values if you still want to do syscalls. This
|
|
* call is more for 32bit mode therefore.
|
|
*/
|
|
struct user_desc {
|
|
unsigned int entry_number;
|
|
unsigned int base_addr;
|
|
unsigned int limit;
|
|
unsigned int seg_32bit:1;
|
|
unsigned int contents:2;
|
|
unsigned int read_exec_only:1;
|
|
unsigned int limit_in_pages:1;
|
|
unsigned int seg_not_present:1;
|
|
unsigned int useable:1;
|
|
#ifdef __x86_64__
|
|
/*
|
|
* Because this bit is not present in 32-bit user code, user
|
|
* programs can pass uninitialized values here. Therefore, in
|
|
* any context in which a user_desc comes from a 32-bit program,
|
|
* the kernel must act as though lm == 0, regardless of the
|
|
* actual value.
|
|
*/
|
|
unsigned int lm:1;
|
|
#endif
|
|
};
|
|
|
|
#define MODIFY_LDT_CONTENTS_DATA 0
|
|
#define MODIFY_LDT_CONTENTS_STACK 1
|
|
#define MODIFY_LDT_CONTENTS_CODE 2
|
|
|
|
#endif /* !__ASSEMBLY__ */
|
|
#endif /* _ASM_X86_LDT_H */
|