File 0240-memory-Revert-memory-accept-mismatc.patch of Package qemu.20395

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File 0240-memory-Revert-memory-accept-mismatc.patch of Package qemu.20395

From: Jose R Ziviani <jose.ziviani@suse.com>
Date: Mon, 10 May 2021 07:57:38 -0600
Subject: memory: Revert "memory: accept mismatching sizes in
 memory_region_access_valid"

Git-commit: 5d971f9e672507210e77d020d89e0e89165c8fc9
References: bsc#1172382 CVE-2020-13754

Memory API documentation documents valid .min_access_size and .max_access_size
fields and explains that any access outside these boundaries is blocked.

This is what devices seem to assume.

However this is not what the implementation does: it simply
ignores the boundaries unless there's an "accepts" callback.

Naturally, this breaks a bunch of devices.

Revert to the documented behaviour.

Devices that want to allow any access can just drop the valid field,
or add the impl field to have accesses converted to appropriate
length.

Cc: qemu-stable@nongnu.org
Reviewed-by: Richard Henderson <rth@twiddle.net>
Fixes: CVE-2020-13754
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1842363
Fixes: a014ed07bd5a ("memory: accept mismatching sizes in memory_region_access_valid")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20200610134731.1514409-1-mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jose R. Ziviani <jose.ziviani@suse.com>
---
 memory.c | 29 +++++++++--------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/memory.c b/memory.c
index e3ff97803191baf5219335184ab6..90ab14c060f670524f6befac6806 100644
--- a/memory.c
+++ b/memory.c
@@ -1349,35 +1349,24 @@ bool memory_region_access_valid(MemoryRegion *mr,
                                 unsigned size,
                                 bool is_write)
 {
-    int access_size_min, access_size_max;
-    int access_size, i;
-
-    if (!mr->ops->valid.unaligned && (addr & (size - 1))) {
+    if (mr->ops->valid.accepts
+        && !mr->ops->valid.accepts(mr->opaque, addr, size, is_write)) {
         return false;
     }
 
-    if (!mr->ops->valid.accepts) {
-        return true;
-    }
-
-    access_size_min = mr->ops->valid.min_access_size;
-    if (!mr->ops->valid.min_access_size) {
-        access_size_min = 1;
+    if (!mr->ops->valid.unaligned && (addr & (size - 1))) {
+        return false;
     }
 
-    access_size_max = mr->ops->valid.max_access_size;
+    /* Treat zero as compatibility all valid */
     if (!mr->ops->valid.max_access_size) {
-        access_size_max = 4;
+        return true;
     }
 
-    access_size = MAX(MIN(size, access_size_max), access_size_min);
-    for (i = 0; i < size; i += access_size) {
-        if (!mr->ops->valid.accepts(mr->opaque, addr + i, access_size,
-                                    is_write)) {
-            return false;
-        }
+    if (size > mr->ops->valid.max_access_size
+        || size < mr->ops->valid.min_access_size) {
+        return false;
     }
-
     return true;
 }

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File 0240-memory-Revert-memory-accept-mismatc.patch of Package qemu.20395

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