Description
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O When completing emulation of instruction that generated a userspace exit for I/O, don't recheck L1 intercepts as KVM has already finished that phase of instruction execution, i.e. has already committed to allowing L2 to perform I/O. If L1 (or host userspace) modifies the I/O permission bitmaps during the exit to userspace, KVM will treat the access as being intercepted despite already having emulated the I/O access. Pivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation. Of the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the intended "recipient") can reach the code in question. gp_interception()'s use is mutually exclusive with is_guest_mode(), and complete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with EMULTYPE_SKIP. The bad behavior was detected by a syzkaller program that toggles port I/O interception during the userspace I/O exit, ultimately resulting in a WARN on vcpu->arch.pio.count being non-zero due to KVM no completing emulation of the I/O instruction. WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm] Modules linked in: kvm_intel kvm irqbypass CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm] PKRU: 55555554 Call Trace: <TASK> kvm_fast_pio+0xd6/0x1d0 [kvm] vmx_handle_exit+0x149/0x610 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm] kvm_vcpu_ioctl+0x244/0x8c0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0x5d/0xc60 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK>
Product status
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before a908eca437789589dd4624da428614c1275064dc
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before 00338255bb1f422642fb2798ebe92e93b6e4209b
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before e0ce3ed1048a47986d15aef1a98ebda25560d257
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before ba35a5d775799ce5ad60230be97336f2fefd518e
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before 3d3abf3f7e8b1abb082070a343de82d7efc80523
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before e7177c7e32cb806f348387b7f4faafd4a5b32054
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before 3a062a5c55adc5507600b9ae6d911e247e2f1d6e
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before 7366830642505683bbe905a2ba5d18d6e4b512b8
8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9 (git) before e750f85391286a4c8100275516973324b621a269
3.0
Any version before 3.0
5.4.301 (semver)
5.10.246 (semver)
5.15.195 (semver)
6.1.157 (semver)
6.6.111 (semver)
6.12.52 (semver)
6.16.12 (semver)
6.17.2 (semver)
6.18-rc1 (original_commit_for_fix)
References
git.kernel.org/...c/a908eca437789589dd4624da428614c1275064dc
git.kernel.org/...c/00338255bb1f422642fb2798ebe92e93b6e4209b
git.kernel.org/...c/e0ce3ed1048a47986d15aef1a98ebda25560d257
git.kernel.org/...c/ba35a5d775799ce5ad60230be97336f2fefd518e
git.kernel.org/...c/3d3abf3f7e8b1abb082070a343de82d7efc80523
git.kernel.org/...c/e7177c7e32cb806f348387b7f4faafd4a5b32054
git.kernel.org/...c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e
git.kernel.org/...c/7366830642505683bbe905a2ba5d18d6e4b512b8
git.kernel.org/...c/e750f85391286a4c8100275516973324b621a269
