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Date: Wed, 26 Feb 2020 18:51:02 +0100 From: Vitaly Kuznetsov <vkuznets@...hat.com> To: Sean Christopherson <sean.j.christopherson@...el.com> Cc: Paolo Bonzini <pbonzini@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 10/13] KVM: x86: Shrink the usercopy region of the emulation context Sean Christopherson <sean.j.christopherson@...el.com> writes: > 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@...el.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; Out of pure curiosity, how certain are we that this is going to be enough for userspaces? > 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); -- Vitaly
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