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Before trying to do nested_get_page() in nested_vmx_merge_msr_bitmap(), we have already checked that the MSR bitmap address is valid (4k aligned and within physical limits). SDM doesn't specify what happens if the there is no memory mapped at the valid address, but Intel CPUs treat the situation as if the bitmap was configured to trap all MSRs. KVM already does that by returning false and a correct handling doesn't need the guest-trigerrable warning that was reported by syzkaller: (The warning was originally there to catch some possible bugs in nVMX.) ------------[ cut here ]------------ WARNING: CPU: 0 PID: 7832 at arch/x86/kvm/vmx.c:9709 nested_vmx_merge_msr_bitmap arch/x86/kvm/vmx.c:9709 [inline] WARNING: CPU: 0 PID: 7832 at arch/x86/kvm/vmx.c:9709 nested_get_vmcs12_pages+0xfb6/0x15c0 arch/x86/kvm/vmx.c:9640 Kernel panic - not syncing: panic_on_warn set ... CPU: 0 PID: 7832 Comm: syz-executor1 Not tainted 4.10.0+ #229 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:15 [inline] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51 panic+0x1fb/0x412 kernel/panic.c:179 __warn+0x1c4/0x1e0 kernel/panic.c:540 warn_slowpath_null+0x2c/0x40 kernel/panic.c:583 nested_vmx_merge_msr_bitmap arch/x86/kvm/vmx.c:9709 [inline] nested_get_vmcs12_pages+0xfb6/0x15c0 arch/x86/kvm/vmx.c:9640 enter_vmx_non_root_mode arch/x86/kvm/vmx.c:10471 [inline] nested_vmx_run+0x6186/0xaab0 arch/x86/kvm/vmx.c:10561 handle_vmlaunch+0x1a/0x20 arch/x86/kvm/vmx.c:7312 vmx_handle_exit+0xfc0/0x3f00 arch/x86/kvm/vmx.c:8526 vcpu_enter_guest arch/x86/kvm/x86.c:6982 [inline] vcpu_run arch/x86/kvm/x86.c:7044 [inline] kvm_arch_vcpu_ioctl_run+0x1418/0x4840 arch/x86/kvm/x86.c:7205 kvm_vcpu_ioctl+0x673/0x1120 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2570 Reported-by: Dmitry Vyukov <dvyukov@google.com> Reviewed-by: Jim Mattson <jmattson@google.com> [Jim Mattson explained the bare metal behavior: "I believe this behavior would be documented in the chipset data sheet rather than the SDM, since the chipset returns all 1s for an unclaimed read."] Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> |
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| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.