Patch "RISC-V: KVM: Don't zero-out PMU snapshot area before freeing data" has been added to the 6.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    RISC-V: KVM: Don't zero-out PMU snapshot area before freeing data

to the 6.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     risc-v-kvm-don-t-zero-out-pmu-snapshot-area-before-f.patch
and it can be found in the queue-6.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 9b6a15d36571c728fedde6a86db430db10c2853b
Author: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
Date:   Thu Aug 15 22:39:07 2024 +0530

    RISC-V: KVM: Don't zero-out PMU snapshot area before freeing data
    
    [ Upstream commit 47d40d93292d9cff8dabb735bed83d930fa03950 ]
    
    With the latest Linux-6.11-rc3, the below NULL pointer crash is observed
    when SBI PMU snapshot is enabled for the guest and the guest is forcefully
    powered-off.
    
      Unable to handle kernel NULL pointer dereference at virtual address 0000000000000508
      Oops [#1]
      Modules linked in: kvm
      CPU: 0 UID: 0 PID: 61 Comm: term-poll Not tainted 6.11.0-rc3-00018-g44d7178dd77a #3
      Hardware name: riscv-virtio,qemu (DT)
      epc : __kvm_write_guest_page+0x94/0xa6 [kvm]
       ra : __kvm_write_guest_page+0x54/0xa6 [kvm]
      epc : ffffffff01590e98 ra : ffffffff01590e58 sp : ffff8f80001f39b0
       gp : ffffffff81512a60 tp : ffffaf80024872c0 t0 : ffffaf800247e000
       t1 : 00000000000007e0 t2 : 0000000000000000 s0 : ffff8f80001f39f0
       s1 : 00007fff89ac4000 a0 : ffffffff015dd7e8 a1 : 0000000000000086
       a2 : 0000000000000000 a3 : ffffaf8000000000 a4 : ffffaf80024882c0
       a5 : 0000000000000000 a6 : ffffaf800328d780 a7 : 00000000000001cc
       s2 : ffffaf800197bd00 s3 : 00000000000828c4 s4 : ffffaf800248c000
       s5 : ffffaf800247d000 s6 : 0000000000001000 s7 : 0000000000001000
       s8 : 0000000000000000 s9 : 00007fff861fd500 s10: 0000000000000001
       s11: 0000000000800000 t3 : 00000000000004d3 t4 : 00000000000004d3
       t5 : ffffffff814126e0 t6 : ffffffff81412700
      status: 0000000200000120 badaddr: 0000000000000508 cause: 000000000000000d
      [<ffffffff01590e98>] __kvm_write_guest_page+0x94/0xa6 [kvm]
      [<ffffffff015943a6>] kvm_vcpu_write_guest+0x56/0x90 [kvm]
      [<ffffffff015a175c>] kvm_pmu_clear_snapshot_area+0x42/0x7e [kvm]
      [<ffffffff015a1972>] kvm_riscv_vcpu_pmu_deinit.part.0+0xe0/0x14e [kvm]
      [<ffffffff015a2ad0>] kvm_riscv_vcpu_pmu_deinit+0x1a/0x24 [kvm]
      [<ffffffff0159b344>] kvm_arch_vcpu_destroy+0x28/0x4c [kvm]
      [<ffffffff0158e420>] kvm_destroy_vcpus+0x5a/0xda [kvm]
      [<ffffffff0159930c>] kvm_arch_destroy_vm+0x14/0x28 [kvm]
      [<ffffffff01593260>] kvm_destroy_vm+0x168/0x2a0 [kvm]
      [<ffffffff015933d4>] kvm_put_kvm+0x3c/0x58 [kvm]
      [<ffffffff01593412>] kvm_vm_release+0x22/0x2e [kvm]
    
    Clearly, the kvm_vcpu_write_guest() function is crashing because it is
    being called from kvm_pmu_clear_snapshot_area() upon guest tear down.
    
    To address the above issue, simplify the kvm_pmu_clear_snapshot_area() to
    not zero-out PMU snapshot area from kvm_pmu_clear_snapshot_area() because
    the guest is anyway being tore down.
    
    The kvm_pmu_clear_snapshot_area() is also called when guest changes
    PMU snapshot area of a VCPU but even in this case the previous PMU
    snaphsot area must not be zeroed-out because the guest might have
    reclaimed the pervious PMU snapshot area for some other purpose.
    
    Fixes: c2f41ddbcdd7 ("RISC-V: KVM: Implement SBI PMU Snapshot feature")
    Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240815170907.2792229-1-apatel@xxxxxxxxxxxxxxxx
    Signed-off-by: Anup Patel <anup@xxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
index bcf41d6e0df0e..2707a51b082ca 100644
--- a/arch/riscv/kvm/vcpu_pmu.c
+++ b/arch/riscv/kvm/vcpu_pmu.c
@@ -391,19 +391,9 @@ int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
 static void kvm_pmu_clear_snapshot_area(struct kvm_vcpu *vcpu)
 {
 	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
-	int snapshot_area_size = sizeof(struct riscv_pmu_snapshot_data);
 
-	if (kvpmu->sdata) {
-		if (kvpmu->snapshot_addr != INVALID_GPA) {
-			memset(kvpmu->sdata, 0, snapshot_area_size);
-			kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr,
-					     kvpmu->sdata, snapshot_area_size);
-		} else {
-			pr_warn("snapshot address invalid\n");
-		}
-		kfree(kvpmu->sdata);
-		kvpmu->sdata = NULL;
-	}
+	kfree(kvpmu->sdata);
+	kvpmu->sdata = NULL;
 	kvpmu->snapshot_addr = INVALID_GPA;
 }