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x86/entry/32: Fix FIXUP_ESPFIX_STACK with user CR3 

UNWIND_ESPFIX_STACK needs to read the GDT, and the GDT mapping that
can be accessed via %fs is not mapped in the user pagetables.  Use
SGDT to find the cpu_entry_area mapping and read the espfix offset
from that instead.

Reported-and-tested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2019-11-24 08:50:03 -08:00 committed by Ingo Molnar
parent 05b042a194
commit 4a13b0e3e1
1 changed files with 18 additions and 3 deletions
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21
arch/x86/entry/entry_32.S
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@ -415,7 +415,8 @@
.macro CHECK_AND_APPLY_ESPFIX
#ifdef CONFIG_X86_ESPFIX32
#define GDT_ESPFIX_SS PER_CPU_VAR(gdt_page) + (GDT_ENTRY_ESPFIX_SS * 8)
#define GDT_ESPFIX_OFFSET (GDT_ENTRY_ESPFIX_SS * 8)
#define GDT_ESPFIX_SS PER_CPU_VAR(gdt_page) + GDT_ESPFIX_OFFSET
ALTERNATIVE "jmp .Lend_\@", "", X86_BUG_ESPFIX
@ -1147,12 +1148,26 @@ ENDPROC(entry_INT80_32)
* We can't call C functions using the ESPFIX stack. This code reads
* the high word of the segment base from the GDT and swiches to the
* normal stack and adjusts ESP with the matching offset.
*
* We might be on user CR3 here, so percpu data is not mapped and we can't
* access the GDT through the percpu segment. Instead, use SGDT to find
* the cpu_entry_area alias of the GDT.
*/
#ifdef CONFIG_X86_ESPFIX32
/* fixup the stack */
mov GDT_ESPFIX_SS + 4, %al /* bits 16..23 */
mov GDT_ESPFIX_SS + 7, %ah /* bits 24..31 */
pushl %ecx
subl $2*4, %esp
sgdt (%esp)
movl 2(%esp), %ecx /* GDT address */
/*
* Careful: ECX is a linear pointer, so we need to force base
* zero. %cs is the only known-linear segment we have right now.
*/
mov %cs:GDT_ESPFIX_OFFSET + 4(%ecx), %al /* bits 16..23 */
mov %cs:GDT_ESPFIX_OFFSET + 7(%ecx), %ah /* bits 24..31 */
shl $16, %eax
addl $2*4, %esp
popl %ecx
addl %esp, %eax /* the adjusted stack pointer */
pushl $__KERNEL_DS
pushl %eax