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

Message ID 20191122223959.13545-11-sean.j.christopherson@intel.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86: Allow userspace to disable the emulator | expand

Commit Message

Sean Christopherson Nov. 22, 2019, 10:39 p.m. UTC 
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(-)
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Patch

diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 844e833609db..c25133080666 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -318,9 +318,6 @@  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);
 	/*
@@ -345,6 +342,11 @@  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 548cf3b659f5..418717876ad0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -231,13 +231,13 @@  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);