[PATCH 6.12.y] KVM: nSVM: Check validity of vmcs01 save area copied from SMRAM on RSM

[Sasha Levin <sashal@kernel.org>]

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit 053621535f014085c935879582dd3b65964a0dce ]

When doing RSM to L2, validate L1's state after copying it back into vmcb01
from SMRAM, as SMRAM is carved out of guest memory, i.e. is writable by the
guest.  Failure to validate L1's state is especially problematic for inputs
to MMU context, as KVM can end up with impossible CR4 vs. EFER state.  E.g.
without the recent hardening FNAME(walk_addr_generic), a guest can trigger:

  ------------[ cut here ]------------
  UBSAN: array-index-out-of-bounds in arch/x86/kvm/mmu/paging_tmpl.h:435:15
  index 3 is out of range for type 'u32 [2]'
  CPU: 3 UID: 0 PID: 92 Comm: CPU 1/KVM Not tainted 7.3.0-rc1 #2 PREEMPT(lazy)
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
  Call Trace:
   <TASK>
   dump_stack_lvl+0x5f/0x90
   dump_stack+0x10/0x18
   ubsan_epilogue+0x9/0x39
   __ubsan_handle_out_of_bounds.cold+0x50/0x55
   paging32_walk_addr_generic+0x889/0x970
   paging32_page_fault+0x79/0xa60
   kvm_mmu_do_page_fault+0x125/0x270
   kvm_mmu_page_fault+0x88/0x7b0
   npf_interception+0xc8/0x220 [kvm_amd]
   svm_invoke_exit_handler+0x16d/0x1d0 [kvm_amd]
   svm_handle_exit+0xb7/0x160 [kvm_amd]
   vcpu_enter_guest+0x428/0x16a0
   kvm_arch_vcpu_ioctl_run+0x479/0x920
   kvm_vcpu_ioctl+0x316/0xb00
   __x64_sys_ioctl+0xa3/0x100
   x64_sys_call+0x281/0x23d0
   do_syscall_64+0xba/0x550
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
  RIP: 0033:0x79bb30deb04b
   </TASK>
  ---[ end trace ]---

Fixes: 37be407b2ce8 ("KVM: nSVM: Fix L1 state corruption upon return from SMM")
Cc: stable@vger.kernel.org
Reported-by: Bill Wendling <morbo@google.com>
Reported-by: Stefan Teodorescu <fane@google.com>
Tested-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20261022021046.295001-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[ sashal: adapted validation to __nested_vmcb_check_save() with failures routed through the existing unmap_save cleanup ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/svm/nested.c | 23 ++++++++++++++++-------
 arch/x86/kvm/svm/svm.c    |  2 ++
 arch/x86/kvm/svm/svm.h    |  2 ++
 3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 3c9c20d7855fe..670a5d57f33da 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1613,6 +1613,21 @@ static void nested_copy_vmcb_cache_to_control(struct vmcb_control_area *dst,
 	/* 'clean' and 'hv_enlightenments' are not changed by KVM */
 }
 
+bool nested_svm_check_vmcb01_save(struct kvm_vcpu *vcpu,
+				  struct vmcb_save_area *save)
+{
+	struct vmcb_save_area_cached save_cached;
+
+	if (!(save->cr0 & X86_CR0_PG) ||
+	    !(save->cr0 & X86_CR0_PE) ||
+	    (save->rflags & X86_EFLAGS_VM) ||
+	    ((save->efer & EFER_LMA) && !(save->efer & EFER_LME)))
+		return false;
+
+	__nested_copy_vmcb_save_to_cache(&save_cached, save);
+	return __nested_vmcb_check_save(vcpu, &save_cached);
+}
+
 static int svm_get_nested_state(struct kvm_vcpu *vcpu,
 				struct kvm_nested_state __user *user_kvm_nested_state,
 				u32 user_data_size)
@@ -1689,7 +1704,6 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 		&user_kvm_nested_state->data.svm[0];
 	struct vmcb_control_area *ctl;
 	struct vmcb_save_area *save;
-	struct vmcb_save_area_cached save_cached;
 	struct vmcb_ctrl_area_cached ctl_cached;
 	unsigned long cr0;
 	int ret;
@@ -1759,12 +1773,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	 * Validate host state saved from before VMRUN (see
 	 * nested_svm_check_permissions).
 	 */
-	__nested_copy_vmcb_save_to_cache(&save_cached, save);
-	if (!(save->cr0 & X86_CR0_PG) ||
-	    !(save->cr0 & X86_CR0_PE) ||
-	    (save->rflags & X86_EFLAGS_VM) ||
-	    ((save->efer & EFER_LMA) && !(save->efer & EFER_LME)) ||
-	    !__nested_vmcb_check_save(vcpu, &save_cached))
+	if (!nested_svm_check_vmcb01_save(vcpu, save))
 		goto out_free;
 
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index df325d0864819..2796368f231d3 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4960,6 +4960,8 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram)
 	 */
 
 	svm_copy_vmrun_state(&svm->vmcb01.ptr->save, map_save.hva + 0x400);
+	if (!nested_svm_check_vmcb01_save(vcpu, &svm->vmcb01.ptr->save))
+		goto unmap_save;
 
 	/*
 	 * Enter the nested guest now
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 511fadfb055f6..a3724e867a4c9 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -689,6 +689,8 @@ void nested_copy_vmcb_save_to_cache(struct vcpu_svm *svm,
 				    struct vmcb_save_area *save);
 void nested_sync_control_from_vmcb02(struct vcpu_svm *svm);
 void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm);
+bool nested_svm_check_vmcb01_save(struct kvm_vcpu *vcpu,
+				  struct vmcb_save_area *save);
 void svm_switch_vmcb(struct vcpu_svm *svm, struct kvm_vmcb_info *target_vmcb);
 
 extern struct kvm_x86_nested_ops svm_nested_ops;
-- 
2.53.0