Date: Thu, 28 Oct 2021 05:58:05 +0200 From: Salvatore Bonaccorso <carnil@...ian.org> To: Michael Ellerman <mpe@...erman.id.au> Cc: oss-security@...ts.openwall.com, linuxppc-dev@...ts.ozlabs.org, John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de> Subject: Re: Linux kernel: powerpc: KVM guest can trigger host crash on Power8 Hi, On Mon, Oct 25, 2021 at 10:18:54PM +1100, Michael Ellerman wrote: > The Linux kernel for powerpc since v5.2 has a bug which allows a > malicious KVM guest to crash the host, when the host is running on > Power8. > > Only machines using Linux as the hypervisor, aka. KVM, powernv or bare > metal, are affected by the bug. Machines running PowerVM are not > affected. > > The bug was introduced in: > > 10d91611f426 ("powerpc/64s: Reimplement book3s idle code in C") > > Which was first released in v5.2. > > The upstream fix is: > > cdeb5d7d890e ("KVM: PPC: Book3S HV: Make idle_kvm_start_guest() return 0 if it went to guest") > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cdeb5d7d890e14f3b70e8087e745c4a6a7d9f337 > > Which will be included in the v5.16 release. > > Note to backporters, the following commits are required: > > 73287caa9210ded6066833195f4335f7f688a46b > ("powerpc64/idle: Fix SP offsets when saving GPRs") > > 9b4416c5095c20e110c82ae602c254099b83b72f > ("KVM: PPC: Book3S HV: Fix stack handling in idle_kvm_start_guest()") > > cdeb5d7d890e14f3b70e8087e745c4a6a7d9f337 > ("KVM: PPC: Book3S HV: Make idle_kvm_start_guest() return 0 if it went to guest") > > 496c5fe25c377ddb7815c4ce8ecfb676f051e9b6 > ("powerpc/idle: Don't corrupt back chain when going idle") > > > I have a test case to trigger the bug, which I can share privately with > anyone who would like to test the fix. The issue has been assigned CVE-2021-43056. Regards, Salvatore
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