FAILED: patch "[PATCH] KVM: SVM: Flush pages under kvm->lock to fix UAF in" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x 5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024032701-robotics-energize-d297@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

5ef1d8c1ddbf ("KVM: SVM: Flush pages under kvm->lock to fix UAF in svm_register_enc_region()")
19a23da53932 ("Fix unsynchronized access to sev members through svm_register_enc_region")
a8d908b5873c ("KVM: x86: report sev_pin_memory errors with PTR_ERR")
dc42c8ae0a77 ("KVM: SVM: convert get_user_pages() --> pin_user_pages()")
78824fabc72e ("KVM: SVM: fix svn_pin_memory()'s use of get_user_pages_fast()")
996ed22c7a52 ("arch/x86/kvm/svm/sev.c: change flag passed to GUP fast in sev_pin_memory()")
eaf78265a4ab ("KVM: SVM: Move SEV code to separate file")
ef0f64960d01 ("KVM: SVM: Move AVIC code to separate file")
883b0a91f41a ("KVM: SVM: Move Nested SVM Implementation to nested.c")
46a010dd6896 ("kVM SVM: Move SVM related files to own sub-directory")
8c1b724ddb21 ("Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Fri, 16 Feb 2024 17:34:30 -0800
Subject: [PATCH] KVM: SVM: Flush pages under kvm->lock to fix UAF in
 svm_register_enc_region()

Do the cache flush of converted pages in svm_register_enc_region() before
dropping kvm->lock to fix use-after-free issues where region and/or its
array of pages could be freed by a different task, e.g. if userspace has
__unregister_enc_region_locked() already queued up for the region.

Note, the "obvious" alternative of using local variables doesn't fully
resolve the bug, as region->pages is also dynamically allocated.  I.e. the
region structure itself would be fine, but region->pages could be freed.

Flushing multiple pages under kvm->lock is unfortunate, but the entire
flow is a rare slow path, and the manual flush is only needed on CPUs that
lack coherency for encrypted memory.

Fixes: 19a23da53932 ("Fix unsynchronized access to sev members through svm_register_enc_region")
Reported-by: Gabe Kirkpatrick <gkirkpatrick@google.com>
Cc: Josh Eads <josheads@google.com>
Cc: Peter Gonda <pgonda@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20240217013430.2079561-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index f760106c31f8..a132547fcfb5 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1975,20 +1975,22 @@ int sev_mem_enc_register_region(struct kvm *kvm,
 		goto e_free;
 	}
 
+	/*
+	 * The guest may change the memory encryption attribute from C=0 -> C=1
+	 * or vice versa for this memory range. Lets make sure caches are
+	 * flushed to ensure that guest data gets written into memory with
+	 * correct C-bit.  Note, this must be done before dropping kvm->lock,
+	 * as region and its array of pages can be freed by a different task
+	 * once kvm->lock is released.
+	 */
+	sev_clflush_pages(region->pages, region->npages);
+
 	region->uaddr = range->addr;
 	region->size = range->size;
 
 	list_add_tail(&region->list, &sev->regions_list);
 	mutex_unlock(&kvm->lock);
 
-	/*
-	 * The guest may change the memory encryption attribute from C=0 -> C=1
-	 * or vice versa for this memory range. Lets make sure caches are
-	 * flushed to ensure that guest data gets written into memory with
-	 * correct C-bit.
-	 */
-	sev_clflush_pages(region->pages, region->npages);
-
 	return ret;
 
 e_free: