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1d6a821277
On an MMIO access, we always copy the on-stack buffer info the shared "run" structure, even if this is a read access. This ends up leaking up to 8 bytes of uninitialized memory into userspace, depending on the size of the access. An obvious fix for this one is to only perform the copy if this is an actual write. Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
224 lines
5.0 KiB
C
224 lines
5.0 KiB
C
/*
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* Copyright (C) 2012 - Virtual Open Systems and Columbia University
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* Author: Christoffer Dall <c.dall@virtualopensystems.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License, version 2, as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#include <linux/kvm_host.h>
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#include <asm/kvm_mmio.h>
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#include <asm/kvm_emulate.h>
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#include <trace/events/kvm.h>
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#include "trace.h"
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static void mmio_write_buf(char *buf, unsigned int len, unsigned long data)
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{
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void *datap = NULL;
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union {
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u8 byte;
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u16 hword;
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u32 word;
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u64 dword;
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} tmp;
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switch (len) {
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case 1:
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tmp.byte = data;
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datap = &tmp.byte;
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break;
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case 2:
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tmp.hword = data;
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datap = &tmp.hword;
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break;
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case 4:
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tmp.word = data;
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datap = &tmp.word;
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break;
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case 8:
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tmp.dword = data;
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datap = &tmp.dword;
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break;
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}
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memcpy(buf, datap, len);
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}
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static unsigned long mmio_read_buf(char *buf, unsigned int len)
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{
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unsigned long data = 0;
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union {
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u16 hword;
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u32 word;
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u64 dword;
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} tmp;
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switch (len) {
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case 1:
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data = buf[0];
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break;
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case 2:
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memcpy(&tmp.hword, buf, len);
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data = tmp.hword;
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break;
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case 4:
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memcpy(&tmp.word, buf, len);
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data = tmp.word;
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break;
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case 8:
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memcpy(&tmp.dword, buf, len);
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data = tmp.dword;
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break;
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}
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return data;
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}
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/**
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* kvm_handle_mmio_return -- Handle MMIO loads after user space emulation
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* @vcpu: The VCPU pointer
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* @run: The VCPU run struct containing the mmio data
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*
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* This should only be called after returning from userspace for MMIO load
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* emulation.
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*/
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int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
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{
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unsigned long data;
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unsigned int len;
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int mask;
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if (!run->mmio.is_write) {
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len = run->mmio.len;
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if (len > sizeof(unsigned long))
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return -EINVAL;
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data = mmio_read_buf(run->mmio.data, len);
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if (vcpu->arch.mmio_decode.sign_extend &&
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len < sizeof(unsigned long)) {
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mask = 1U << ((len * 8) - 1);
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data = (data ^ mask) - mask;
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}
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trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr,
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data);
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data = vcpu_data_host_to_guest(vcpu, data, len);
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vcpu_set_reg(vcpu, vcpu->arch.mmio_decode.rt, data);
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}
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return 0;
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}
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static int decode_hsr(struct kvm_vcpu *vcpu, bool *is_write, int *len)
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{
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unsigned long rt;
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int access_size;
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bool sign_extend;
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if (kvm_vcpu_dabt_isextabt(vcpu)) {
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/* cache operation on I/O addr, tell guest unsupported */
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kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
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return 1;
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}
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if (kvm_vcpu_dabt_iss1tw(vcpu)) {
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/* page table accesses IO mem: tell guest to fix its TTBR */
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kvm_inject_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
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return 1;
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}
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access_size = kvm_vcpu_dabt_get_as(vcpu);
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if (unlikely(access_size < 0))
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return access_size;
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*is_write = kvm_vcpu_dabt_iswrite(vcpu);
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sign_extend = kvm_vcpu_dabt_issext(vcpu);
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rt = kvm_vcpu_dabt_get_rd(vcpu);
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*len = access_size;
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vcpu->arch.mmio_decode.sign_extend = sign_extend;
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vcpu->arch.mmio_decode.rt = rt;
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/*
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* The MMIO instruction is emulated and should not be re-executed
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* in the guest.
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*/
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kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
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return 0;
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}
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int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
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phys_addr_t fault_ipa)
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{
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unsigned long data;
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unsigned long rt;
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int ret;
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bool is_write;
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int len;
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u8 data_buf[8];
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/*
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* Prepare MMIO operation. First decode the syndrome data we get
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* from the CPU. Then try if some in-kernel emulation feels
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* responsible, otherwise let user space do its magic.
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*/
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if (kvm_vcpu_dabt_isvalid(vcpu)) {
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ret = decode_hsr(vcpu, &is_write, &len);
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if (ret)
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return ret;
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} else {
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kvm_err("load/store instruction decoding not implemented\n");
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return -ENOSYS;
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}
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rt = vcpu->arch.mmio_decode.rt;
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if (is_write) {
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data = vcpu_data_guest_to_host(vcpu, vcpu_get_reg(vcpu, rt),
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len);
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trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, len, fault_ipa, data);
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mmio_write_buf(data_buf, len, data);
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ret = kvm_io_bus_write(vcpu, KVM_MMIO_BUS, fault_ipa, len,
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data_buf);
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} else {
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trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, len,
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fault_ipa, 0);
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ret = kvm_io_bus_read(vcpu, KVM_MMIO_BUS, fault_ipa, len,
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data_buf);
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}
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/* Now prepare kvm_run for the potential return to userland. */
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run->mmio.is_write = is_write;
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run->mmio.phys_addr = fault_ipa;
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run->mmio.len = len;
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if (is_write)
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memcpy(run->mmio.data, data_buf, len);
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if (!ret) {
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/* We handled the access successfully in the kernel. */
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vcpu->stat.mmio_exit_kernel++;
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kvm_handle_mmio_return(vcpu, run);
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return 1;
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} else {
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vcpu->stat.mmio_exit_user++;
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}
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run->exit_reason = KVM_EXIT_MMIO;
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return 0;
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}
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