Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
Merge tag 'x86_urgent_for_v6.2_rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fix from Borislav Petkov:
- Prevent the compiler from reordering accesses to debug regs which
could cause a #VC exception in SEV-ES guests at the wrong place in
the NMI handling path
* tag 'x86_urgent_for_v6.2_rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/debug: Fix stack recursion caused by wrongly ordered DR7 accesses
+24
-2
+24
-2
arch/x86/include/asm/debugreg.h
+24
-2
arch/x86/include/asm/debugreg.h
···
39
39
asm("mov %%db6, %0" :"=r" (val));
40
40
break;
41
41
case 7:
42
-
asm("mov %%db7, %0" :"=r" (val));
42
+
/*
43
+
* Apply __FORCE_ORDER to DR7 reads to forbid re-ordering them
44
+
* with other code.
45
+
*
46
+
* This is needed because a DR7 access can cause a #VC exception
47
+
* when running under SEV-ES. Taking a #VC exception is not a
48
+
* safe thing to do just anywhere in the entry code and
49
+
* re-ordering might place the access into an unsafe location.
50
+
*
51
+
* This happened in the NMI handler, where the DR7 read was
52
+
* re-ordered to happen before the call to sev_es_ist_enter(),
53
+
* causing stack recursion.
54
+
*/
55
+
asm volatile("mov %%db7, %0" : "=r" (val) : __FORCE_ORDER);
43
56
break;
44
57
default:
45
58
BUG();
···
79
66
asm("mov %0, %%db6" ::"r" (value));
80
67
break;
81
68
case 7:
82
-
asm("mov %0, %%db7" ::"r" (value));
69
+
/*
70
+
* Apply __FORCE_ORDER to DR7 writes to forbid re-ordering them
71
+
* with other code.
72
+
*
73
+
* While is didn't happen with a DR7 write (see the DR7 read
74
+
* comment above which explains where it happened), add the
75
+
* __FORCE_ORDER here too to avoid similar problems in the
76
+
* future.
77
+
*/
78
+
asm volatile("mov %0, %%db7" ::"r" (value), __FORCE_ORDER);
83
79
break;
84
80
default:
85
81
BUG();