3.2.97-rc1 review patch. If anyone has any objections, please let me know.
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From: Wanpeng Li wanpeng.li@hotmail.com
commit e39d200fa5bf5b94a0948db0dae44c1b73b84a56 upstream.
Reported by syzkaller:
BUG: KASAN: stack-out-of-bounds in write_mmio+0x11e/0x270 [kvm] Read of size 8 at addr ffff8803259df7f8 by task syz-executor/32298
CPU: 6 PID: 32298 Comm: syz-executor Tainted: G OE 4.15.0-rc2+ #18 Hardware name: LENOVO ThinkCentre M8500t-N000/SHARKBAY, BIOS FBKTC1AUS 02/16/2016 Call Trace: dump_stack+0xab/0xe1 print_address_description+0x6b/0x290 kasan_report+0x28a/0x370 write_mmio+0x11e/0x270 [kvm] emulator_read_write_onepage+0x311/0x600 [kvm] emulator_read_write+0xef/0x240 [kvm] emulator_fix_hypercall+0x105/0x150 [kvm] em_hypercall+0x2b/0x80 [kvm] x86_emulate_insn+0x2b1/0x1640 [kvm] x86_emulate_instruction+0x39a/0xb90 [kvm] handle_exception+0x1b4/0x4d0 [kvm_intel] vcpu_enter_guest+0x15a0/0x2640 [kvm] kvm_arch_vcpu_ioctl_run+0x549/0x7d0 [kvm] kvm_vcpu_ioctl+0x479/0x880 [kvm] do_vfs_ioctl+0x142/0x9a0 SyS_ioctl+0x74/0x80 entry_SYSCALL_64_fastpath+0x23/0x9a
The path of patched vmmcall will patch 3 bytes opcode 0F 01 C1(vmcall) to the guest memory, however, write_mmio tracepoint always prints 8 bytes through *(u64 *)val since kvm splits the mmio access into 8 bytes. This leaks 5 bytes from the kernel stack (CVE-2017-17741). This patch fixes it by just accessing the bytes which we operate on.
Before patch:
syz-executor-5567 [007] .... 51370.561696: kvm_mmio: mmio write len 3 gpa 0x10 val 0x1ffff10077c1010f
After patch:
syz-executor-13416 [002] .... 51302.299573: kvm_mmio: mmio write len 3 gpa 0x10 val 0xc1010f
Reported-by: Dmitry Vyukov dvyukov@google.com Reviewed-by: Darren Kenny darren.kenny@oracle.com Reviewed-by: Marc Zyngier marc.zyngier@arm.com Tested-by: Marc Zyngier marc.zyngier@arm.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Radim Krčmář rkrcmar@redhat.com Cc: Marc Zyngier marc.zyngier@arm.com Cc: Christoffer Dall christoffer.dall@linaro.org Signed-off-by: Wanpeng Li wanpeng.li@hotmail.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com [bwh: Backported to 3.2: - Drop ARM changes - Adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3920,7 +3920,7 @@ static int vcpu_mmio_read(struct kvm_vcp !kvm_iodevice_read(&vcpu->arch.apic->dev, addr, n, v)) && kvm_io_bus_read(vcpu->kvm, KVM_MMIO_BUS, addr, n, v)) break; - trace_kvm_mmio(KVM_TRACE_MMIO_READ, n, addr, *(u64 *)v); + trace_kvm_mmio(KVM_TRACE_MMIO_READ, n, addr, v); handled += n; addr += n; len -= n; @@ -4152,7 +4152,7 @@ static int read_prepare(struct kvm_vcpu if (vcpu->mmio_read_completed) { memcpy(val, vcpu->mmio_data, bytes); trace_kvm_mmio(KVM_TRACE_MMIO_READ, bytes, - vcpu->mmio_phys_addr, *(u64 *)val); + vcpu->mmio_phys_addr, val); vcpu->mmio_read_completed = 0; return 1; } @@ -4174,14 +4174,14 @@ static int write_emulate(struct kvm_vcpu
static int write_mmio(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes, void *val) { - trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, *(u64 *)val); + trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, val); return vcpu_mmio_write(vcpu, gpa, bytes, val); }
static int read_exit_mmio(struct kvm_vcpu *vcpu, gpa_t gpa, void *val, int bytes) { - trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, bytes, gpa, 0); + trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, bytes, gpa, NULL); return X86EMUL_IO_NEEDED; }
--- a/include/trace/events/kvm.h +++ b/include/trace/events/kvm.h @@ -152,7 +152,7 @@ TRACE_EVENT(kvm_ack_irq, { KVM_TRACE_MMIO_WRITE, "write" }
TRACE_EVENT(kvm_mmio, - TP_PROTO(int type, int len, u64 gpa, u64 val), + TP_PROTO(int type, int len, u64 gpa, void *val), TP_ARGS(type, len, gpa, val),
TP_STRUCT__entry( @@ -166,7 +166,10 @@ TRACE_EVENT(kvm_mmio, __entry->type = type; __entry->len = len; __entry->gpa = gpa; - __entry->val = val; + __entry->val = 0; + if (val) + memcpy(&__entry->val, val, + min_t(u32, sizeof(__entry->val), len)); ),
TP_printk("mmio %s len %u gpa 0x%llx val 0x%llx",