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Mon, 28 Sep 2026 06:30:05 -0700 (PDT) From: Ritesh Harjani (IBM) To: Amit Machhiwal , Madhavan Srinivasan , linuxppc-dev@lists.ozlabs.org Cc: Amit Machhiwal , Nicholas Piggin , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Shrikanth Hegde , kvm-ppc@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Gautam Menghani , Harsh Prateek Bora , R Nageswara Sastry , Alexander Graf , linux-hardening@vger.kernel.org, stable@vger.kernel.org, Avi Kivity Subject: Re: [RESEND PATCH 1/3] KVM: PPC: Book3S HV: Add SRCU protection for virtual-mode HPT hcalls In-Reply-To: <20260928122837.8782-2-amachhiw@linux.ibm.com> Date: Mon, 28 Sep 2026 18:57:16 +0530 Message-ID: References: <20260928122837.8782-1-amachhiw@linux.ibm.com> <20260928122837.8782-2-amachhiw@linux.ibm.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Amit Machhiwal writes: > The virtual-mode HPT hcall handlers (H_ENTER, H_REMOVE, H_BULK_REMOVE, > H_CLEAR_REF, H_CLEAR_MOD) call into book3s_hv_rm_mmu.c, which accesses > memslots via kvm_memslots_raw(). kvm_memslots_raw() uses > rcu_dereference_raw_check() to bypass SRCU lockdep annotation checking. > This is safe in real mode because the entire guest entry/exit is wrapped > in srcu_read_lock/unlock inside kvmppc_run_core() and > kvmhv_run_single_vcpu(). > > However, since commit 6165d5dd99db ("KVM: PPC: Book3S HV: add virtual > mode handlers for HPT hcalls and page faults"), these same handlers are > also executed in virtual mode via kvmppc_pseries_do_hcall(), which runs > after SRCU has already been released on guest exit. > > A concurrent KVM_SET_USER_MEMORY_REGION deletion or move can therefore > call synchronize_srcu_expedited() — which does not wait for this thread — > and then kfree(slot) and vfree(slot->arch.rmap) while the hcall handler > still holds a raw pointer to the memslot. lock_rmap() then writes to > freed vmalloc memory, leading to use-after-free and memory corruption. > Because kvm_memslots_raw() suppresses lockdep checks, this race is > entirely silent. > > Fix this by factoring out the 7 HPT hcall handlers (H_REMOVE, H_ENTER, > H_READ, H_CLEAR_MOD, H_CLEAR_REF, H_PROTECT, H_BULK_REMOVE) into a > helper function, kvmppc_pseries_do_hpt_hcall(), and wrapping its call > site in srcu_read_lock(&kvm->srcu) / srcu_read_unlock(&kvm->srcu, idx). > Targeting only the HPT hcalls avoids wrapping non-HPT hcalls that sleep > (such as H_CONFER, H_REGISTER_VPA, H_PAGE_INIT) or handlers that already > acquire SRCU internally (such as H_RTAS). > > Fixes: 6165d5dd99db ("KVM: PPC: Book3S HV: add virtual mode handlers for HPT hcalls and page faults") > Cc: stable@vger.kernel.org # v5.14+ > Suggested-by: Ritesh Harjani (IBM) > Signed-off-by: Amit Machhiwal > --- > arch/powerpc/kvm/book3s_hv.c | 70 ++++++++++++++++++------------------ > 1 file changed, 35 insertions(+), 35 deletions(-) I had looked at this path in depth earlier itself. LGTM. Please feel free to add: Reviewed-by: Ritesh Harjani (IBM)