Re: [PATCH v7 01/72] KVM: SVM: nested: Don't allocate VMCB structures on stack

[Michael Roth]

Quoting Joerg Roedel (2020-09-07 08:15:02)
> From: Joerg Roedel <jroedel@xxxxxxx>
> 
> Do not allocate a vmcb_control_area and a vmcb_save_area on the stack,
> as these structures will become larger with future extenstions of
> SVM and thus the svm_set_nested_state() function will become a too large
> stack frame.
> 
> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> ---
>  arch/x86/kvm/svm/nested.c | 47 +++++++++++++++++++++++++++------------
>  1 file changed, 33 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index fb68467e6049..28036629abf8 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1060,10 +1060,14 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>         struct vmcb *hsave = svm->nested.hsave;
>         struct vmcb __user *user_vmcb = (struct vmcb __user *)
>                 &user_kvm_nested_state->data.svm[0];
> -       struct vmcb_control_area ctl;
> -       struct vmcb_save_area save;
> +       struct vmcb_control_area *ctl;
> +       struct vmcb_save_area *save;
> +       int ret;
>         u32 cr0;
> 
> +       BUILD_BUG_ON(sizeof(struct vmcb_control_area) + sizeof(struct vmcb_save_area) >
> +                    KVM_STATE_NESTED_SVM_VMCB_SIZE);
> +
>         if (kvm_state->format != KVM_STATE_NESTED_FORMAT_SVM)
>                 return -EINVAL;
> 
> @@ -1095,13 +1099,22 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>                 return -EINVAL;
>         if (kvm_state->size < sizeof(*kvm_state) + KVM_STATE_NESTED_SVM_VMCB_SIZE)
>                 return -EINVAL;
> -       if (copy_from_user(&ctl, &user_vmcb->control, sizeof(ctl)))
> -               return -EFAULT;
> -       if (copy_from_user(&save, &user_vmcb->save, sizeof(save)))
> -               return -EFAULT;
> 
> -       if (!nested_vmcb_check_controls(&ctl))
> -               return -EINVAL;
> +       ret  = -ENOMEM;
> +       ctl  = kzalloc(sizeof(*ctl),  GFP_KERNEL);
> +       save = kzalloc(sizeof(*save), GFP_KERNEL);
> +       if (!ctl || !save)
> +               goto out_free;
> +
> +       ret = -EFAULT;
> +       if (copy_from_user(ctl, &user_vmcb->control, sizeof(*ctl)))
> +               goto out_free;
> +       if (copy_from_user(save, &user_vmcb->save, sizeof(*save)))
> +               goto out_free;
> +
> +       ret = -EINVAL;
> +       if (!nested_vmcb_check_controls(ctl))
> +               goto out_free;
> 
>         /*
>          * Processor state contains L2 state.  Check that it is
> @@ -1109,15 +1122,15 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>          */
>         cr0 = kvm_read_cr0(vcpu);
>          if (((cr0 & X86_CR0_CD) == 0) && (cr0 & X86_CR0_NW))
> -                return -EINVAL;
> +               goto out_free;
> 
>         /*
>          * Validate host state saved from before VMRUN (see
>          * nested_svm_check_permissions).
>          * TODO: validate reserved bits for all saved state.
>          */
> -       if (!(save.cr0 & X86_CR0_PG))
> -               return -EINVAL;
> +       if (!(save->cr0 & X86_CR0_PG))
> +               goto out_free;
> 
>         /*
>          * All checks done, we can enter guest mode.  L1 control fields
> @@ -1126,15 +1139,21 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>          * contains saved L1 state.
>          */
>         copy_vmcb_control_area(&hsave->control, &svm->vmcb->control);
> -       hsave->save = save;
> +       hsave->save = *save;
> 
>         svm->nested.vmcb = kvm_state->hdr.svm.vmcb_pa;
> -       load_nested_vmcb_control(svm, &ctl);
> +       load_nested_vmcb_control(svm, ctl);
>         nested_prepare_vmcb_control(svm);
> 
>  out_set_gif:
>         svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));
> -       return 0;
> +
> +       ret = 0;
> +out_free:
> +       kfree(save);
> +       kfree(ctl);

This change seems to trigger a crash via smm-test.c (and state-test.c) KVM
selftest when we call vcpu_load_state->KVM_SET_NESTED_STATE. I think what's
happening is we are hitting the 'goto out_set_gif;' and then attempting to
free save and ctl, which are still uninitialized at that point: 

[ 1999.801176] APIC base relocation is unsupported by KVM
[ 1999.828562] BUG: unable to handle page fault for address:
fffff12379020288
[ 1999.841968] #PF: supervisor read access in kernel mode
[ 1999.847693] #PF: error_code(0x0000) - not-present page
[ 1999.853426] PGD 0 P4D 0
[ 1999.856252] Oops: 0000 [#1] SMP NOPTI
[ 1999.861366] CPU: 112 PID: 10162 Comm: smm_test Tainted: G
E     5.9.1-amdsos-build31t0+ #1
[ 1999.871655] Hardware name: AMD Corporation ETHANOL_X/ETHANOL_X, BIOS
RXM0092B 10/27/2020
[ 1999.880694] RIP: 0010:kfree+0x5b/0x3c0
[ 1999.884876] Code: 80 49 01 dc 0f 82 70 03 00 00 48 c7 c0 00 00 00 80
48 2b 05 97 4a 1c 01 49 01 c4 49 c1 ec 0c 49 c1 e4 06 4c 03 25 75 4a 1c
01 <49> 8b 44 24 08 48 8d 50 ff a8 01 4c 0f 45 e2 49 8b 54 24 08 48 8d
[ 1999.906674] RSP: 0018:ffffb7004d9d3cf8 EFLAGS: 00010282
[ 1999.912502] RAX: 0000723d80000000 RBX: 000000004080aebf RCX:
0000000002000000
[ 1999.920464] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
000000004080aebf
[ 1999.929335] RBP: ffffb7004d9d3d28 R08: ffff8de1c2a43628 R09:
0000000000000000
[ 1999.937298] R10: 0000000000000000 R11: 0000000000000000 R12:
fffff12379020280
[ 1999.945258] R13: ffffffffc0f6626a R14: 0000000000000000 R15:
ffffb7004d9d3db0
[ 1999.953221] FS:  00007f231b4c1740(0000) GS:ffff8de20e800000(0000)
knlGS:0000000000000000
[ 1999.963255] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1999.969667] CR2: fffff12379020288 CR3: 0000001faf5aa006 CR4:
0000000000770ee0
[ 1999.977627] PKRU: 55555554
[ 1999.980644] Call Trace:
[ 1999.983384]  svm_leave_nested+0xea/0x2f0 [kvm_amd]
[ 1999.988743]  kvm_arch_vcpu_ioctl+0x6fd/0x1260 [kvm]
[ 1999.995026]  ? avic_vcpu_load+0x20/0x130 [kvm_amd]
[ 2000.000372]  kvm_vcpu_kick+0x705/0xae0 [kvm]
[ 2000.005216]  __x64_sys_ioctl+0x91/0xc0
[ 2000.009470]  do_syscall_64+0x38/0x90
[ 2000.013461]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 2000.019090] RIP: 0033:0x7f231b5db50b
[ 2000.024052] Code: 0f 1e fa 48 8b 05 85 39 0d 00 64 c7 00 26 00 00 00
48 c7 c0 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa b8 10 00 00 00 0f
05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 55 39 0d 00 f7 d8 64 89 01 48
[ 2000.045005] RSP: 002b:00007ffc01de6918 EFLAGS: 00000246 ORIG_RAX:
0000000000000010
[ 2000.053453] RAX: ffffffffffffffda RBX: 0000000002147880 RCX:
00007f231b5db50b
[ 2000.062375] RDX: 0000000002148c98 RSI: 000000004080aebf RDI:
0000000000000009
[ 2000.070335] RBP: 000000000214d0c0 R08: 00000000004103f8 R09:
0000000000000000
[ 2000.078296] R10: 0000000000000000 R11: 0000000000000246 R12:
00007ffc01de6960
[ 2000.087278] R13: 0000000000000002 R14: 00007f231b711000 R15:
0000000002147880
[ 2000.095244] Modules linked in: nls_iso8859_1(E) dm_multipath(E)
scsi_dh_rdac(E) scsi_dh_emc(E) scsi_dh_alua(E) intel_rapl_msr(E)
intel_rapl_common(E) amd64_edac_mod(E) kvm_amd(E) kvm(E) joydev(E)
input_leds(E) crct10dif_pclmul(E) crc32_pclmul(E) ghash_clmulni_intel(E)
aesni_intel(E) crypto_simd(E) cryptd(E) glue_helper(E) hid_generic(E)
efi_pstore(E) rapl(E) ipmi_si(E) ipmi_devintf(E) ipmi_msghandler(E)
usbhid(E) hid(E) ast(E) drm_vram_helper(E) drm_ttm_helper(E) ttm(E)
drm_kms_helper(E) cec(E) i2c_algo_bit(E) fb_sys_fops(E) syscopyarea(E)
sysfillrect(E) sysimgblt(E) wmi_bmof(E) e1000e(E) i2c_piix4(E) ccp(E)
wmi(E) mac_hid(E) sch_fq_codel(E) drm(E) ip_tables(E) x_tables(E)
autofs4(E)
[ 2000.164824] CR2: fffff12379020288
[ 2000.168522] ---[ end trace c5975ced3c660340 ]---

> +
> +       return ret;
>  }
> 
>  struct kvm_x86_nested_ops svm_nested_ops = {
> -- 
> 2.28.0
> 
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