diff options
| author | Andy Lutomirski <luto@kernel.org> | 2019-11-24 08:50:03 -0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-11-25 09:36:47 +0100 |
| commit | 4a13b0e3e10996b9aa0b45a764ecfe49f6fcd360 (patch) | |
| tree | b7f1190c4712e52a4eeb867c98286f15da644845 /arch/x86/entry/entry_32.S | |
| parent | 05b042a1944322844eaae7ea596d5f154166d68a (diff) | |
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>
Diffstat (limited to 'arch/x86/entry/entry_32.S')
| -rw-r--r-- | arch/x86/entry/entry_32.S | 21 |
1 files changed, 18 insertions, 3 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 0b8c93136650..f07baf0388bc 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -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 |