Date: Tue, 27 Jul 2021 10:46:14 +1000 From: Michael Ellerman <mpe@...erman.id.au> To: oss-security@...ts.openwall.com Cc: linuxppc-dev@...ts.ozlabs.org Subject: Re: Linux kernel: powerpc: KVM guest to host memory corruption Michael Ellerman <mpe@...erman.id.au> writes: > The Linux kernel for powerpc since v3.10 has a bug which allows a malicious KVM guest to > corrupt host memory. > > In the handling of the H_RTAS hypercall, args.rets is made to point into the args.args > buffer which is located on the stack: > > args.rets = &args.args[be32_to_cpu(args.nargs)]; > > However args.nargs has not been range checked. That allows the guest to point args.rets > anywhere up to +16GB from args.args. > > The guest does not have control of what is written to args.rets, it is always (u32)-3, > because subsequent code does check nargs. Additionally the guest will be killed as a > result of the nargs being out of range, so a given guest only has a single shot at > corrupting memory. > > Only machines using Linux as the hypervisor, aka. KVM or bare metal, are affected by the > bug. > > The bug was introduced in: > > 8e591cb72047 ("KVM: PPC: Book3S: Add infrastructure to implement kernel-side RTAS calls") > > Which was first released in v3.10. > > The upstream fix is: > > f62f3c20647e ("KVM: PPC: Book3S: Fix H_RTAS rets buffer overflow") > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f62f3c20647ebd5fb6ecb8f0b477b9281c44c10a > > Which will be included in the v5.14 release. This has been assigned CVE-2021-37576. cheers
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