[PATCH v2 10/13] KVM: x86: Shrink the usercopy region of the emulation context

Sean Christopherson
2020-02-18T23:30:23Z

Shuffle a few operand structs to the end of struct x86_emulate_ctxt and
update the cache creation to whitelist only the region of the emulation
context that is expected to be copied to/from user memory, e.g. the
instruction operands, registers, and fetch/io/mem caches.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/kvm_emulate.h | 8 +++++---
arch/x86/kvm/x86.c | 12 ++++++------
2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 2f0a600efdff..82f712d5c692 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -322,9 +322,6 @@ struct x86_emulate_ctxt {
u8 intercept;
u8 op_bytes;
u8 ad_bytes;
- struct operand src;
- struct operand src2;
- struct operand dst;
int (*execute)(struct x86_emulate_ctxt *ctxt);
int (*check_perm)(struct x86_emulate_ctxt *ctxt);
/*
@@ -349,6 +346,11 @@ struct x86_emulate_ctxt {
u8 seg_override;
u64 d;
unsigned long _eip;
+
+ /* Here begins the usercopy section. */
+ struct operand src;
+ struct operand src2;
+ struct operand dst;
struct operand memop;
/* Fields above regs are cleared together. */
unsigned long _regs[NR_VCPU_REGS];
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 370af9fe0f5b..e1eaca65756b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -235,13 +235,13 @@ static struct kmem_cache *x86_emulator_cache;

static struct kmem_cache *kvm_alloc_emulator_cache(void)
{
- return kmem_cache_create_usercopy("x86_emulator",
- sizeof(struct x86_emulate_ctxt),
+ unsigned int useroffset = offsetof(struct x86_emulate_ctxt, src);
+ unsigned int size = sizeof(struct x86_emulate_ctxt);
+
+ return kmem_cache_create_usercopy("x86_emulator", size,
__alignof__(struct x86_emulate_ctxt),
- SLAB_ACCOUNT,
- 0,
- sizeof(struct x86_emulate_ctxt),
- NULL);
+ SLAB_ACCOUNT, useroffset,
+ size - useroffset, NULL);
}

static int emulator_fix_hypercall(struct x86_emulate_ctxt *ctxt);
--
2.24.1