linux-kernel - Re: [PATCH 3.4 152/177] KVM: x86: Fix uninitialized op->type for some immediate values

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Message-Id: <861C01D3-25A0-4411-9FBF-C72128CF3EBC@gmail.com>
Date:	Wed, 28 Jan 2015 10:47:02 +0200
From:	Nadav Amit <nadav.amit@...il.com>
To:	lizf@...nel.org
Cc:	stable@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Nadav Amit <namit@...technion.ac.il>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Zefan Li <lizefan@...wei.com>
Subject: Re: [PATCH 3.4 152/177] KVM: x86: Fix uninitialized op->type for some immediate values

This bug should have no effect on Linux 3.4. It shouldn’t hurt, but the
problem it fixes was introduced in 3.16 or 3.17.

Nadav

lizf@...nel.org wrote:

> From: Nadav Amit <namit@...technion.ac.il>
> 
> 3.4.106-rc1 review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> 
> commit d29b9d7ed76c0b961603ca692b8a562556a20212 upstream.
> 
> The emulator could reuse an op->type from a previous instruction for some
> immediate values.  If it mistakenly considers the operands as memory
> operands, it will performs a memory read and overwrite op->val.
> 
> Consider for instance the ROR instruction - src2 (the number of times)
> would be read from memory instead of being used as immediate.
> 
> Mark every immediate operand as such to avoid this problem.
> 
> Fixes: c44b4c6ab80eef3a9c52c7b3f0c632942e6489aa
> Signed-off-by: Nadav Amit <namit@...technion.ac.il>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Zefan Li <lizefan@...wei.com>
> ---
> arch/x86/kvm/emulate.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index e125c3e..0a12507 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -3833,6 +3833,7 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
> 		fetch_register_operand(op);
> 		break;
> 	case OpCL:
> +		op->type = OP_IMM;
> 		op->bytes = 1;
> 		op->val = ctxt->regs[VCPU_REGS_RCX] & 0xff;
> 		break;
> @@ -3840,6 +3841,7 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
> 		rc = decode_imm(ctxt, op, 1, true);
> 		break;
> 	case OpOne:
> +		op->type = OP_IMM;
> 		op->bytes = 1;
> 		op->val = 1;
> 		break;
> @@ -3879,21 +3881,27 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
> 		ctxt->memop.bytes = ctxt->op_bytes + 2;
> 		goto mem_common;
> 	case OpES:
> +		op->type = OP_IMM;
> 		op->val = VCPU_SREG_ES;
> 		break;
> 	case OpCS:
> +		op->type = OP_IMM;
> 		op->val = VCPU_SREG_CS;
> 		break;
> 	case OpSS:
> +		op->type = OP_IMM;
> 		op->val = VCPU_SREG_SS;
> 		break;
> 	case OpDS:
> +		op->type = OP_IMM;
> 		op->val = VCPU_SREG_DS;
> 		break;
> 	case OpFS:
> +		op->type = OP_IMM;
> 		op->val = VCPU_SREG_FS;
> 		break;
> 	case OpGS:
> +		op->type = OP_IMM;
> 		op->val = VCPU_SREG_GS;
> 		break;
> 	case OpImplicit:
> -- 
> 1.9.1


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