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KVM: x86: Use __try_cmpxchg_user() to emulate atomic accesses

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Use the recently introduce __try_cmpxchg_user() to emulate atomic guest
accesses via the associated userspace address instead of mapping the
backing pfn into kernel address space.  Using kvm_vcpu_map() is unsafe as
it does not coordinate with KVM's mmu_notifier to ensure the hva=>pfn
translation isn't changed/unmapped in the memremap() path, i.e. when
there's no struct page and thus no elevated refcount.

Fixes: 42e35f8072 ("KVM/X86: Use kvm_vcpu_map in emulator_cmpxchg_emulated")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220202004945.2540433-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-02-02 00:49:44 +00:00 committed by Paolo Bonzini
parent f122dfe447
commit 1c2361f667
1 changed files with 14 additions and 21 deletions
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35
arch/x86/kvm/x86.c
View File

@ -7257,15 +7257,8 @@ static int emulator_write_emulated(struct x86_emulate_ctxt *ctxt,
exception, &write_emultor);
}
#define CMPXCHG_TYPE(t, ptr, old, new) \
(cmpxchg((t *)(ptr), *(t *)(old), *(t *)(new)) == *(t *)(old))
#ifdef CONFIG_X86_64
# define CMPXCHG64(ptr, old, new) CMPXCHG_TYPE(u64, ptr, old, new)
#else
# define CMPXCHG64(ptr, old, new) \
(cmpxchg64((u64 *)(ptr), *(u64 *)(old), *(u64 *)(new)) == *(u64 *)(old))
#endif
#define emulator_try_cmpxchg_user(t, ptr, old, new) \
(__try_cmpxchg_user((t __user *)(ptr), (t *)(old), *(t *)(new), efault ## t))
static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
unsigned long addr,
@ -7274,12 +7267,11 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
unsigned int bytes,
struct x86_exception *exception)
{
struct kvm_host_map map;
struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
u64 page_line_mask;
unsigned long hva;
gpa_t gpa;
char *kaddr;
bool exchanged;
int r;
/* guests cmpxchg8b have to be emulated atomically */
if (bytes > 8 || (bytes & (bytes - 1)))
@ -7303,31 +7295,32 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask))
goto emul_write;
if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map))
hva = kvm_vcpu_gfn_to_hva(vcpu, gpa_to_gfn(gpa));
if (kvm_is_error_hva(addr))
goto emul_write;
kaddr = map.hva + offset_in_page(gpa);
hva += offset_in_page(gpa);
switch (bytes) {
case 1:
exchanged = CMPXCHG_TYPE(u8, kaddr, old, new);
r = emulator_try_cmpxchg_user(u8, hva, old, new);
break;
case 2:
exchanged = CMPXCHG_TYPE(u16, kaddr, old, new);
r = emulator_try_cmpxchg_user(u16, hva, old, new);
break;
case 4:
exchanged = CMPXCHG_TYPE(u32, kaddr, old, new);
r = emulator_try_cmpxchg_user(u32, hva, old, new);
break;
case 8:
exchanged = CMPXCHG64(kaddr, old, new);
r = emulator_try_cmpxchg_user(u64, hva, old, new);
break;
default:
BUG();
}
kvm_vcpu_unmap(vcpu, &map, true);
if (!exchanged)
if (r < 0)
goto emul_write;
if (r)
return X86EMUL_CMPXCHG_FAILED;
kvm_page_track_write(vcpu, gpa, new, bytes);