[Xen-changelog] [xen stable-4.12] EFI: re-check {get, set}-variable name strings after copying in

[patchbot@xxxxxxx]

commit 636b40dcd50f8e348a9f159d3fe0ad9387879997
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Mar 5 11:19:02 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 5 11:19:02 2020 +0100

    EFI: re-check {get,set}-variable name strings after copying in
    
    A malicious guest given permission to invoke XENPF_efi_runtime_call may
    play with the strings underneath Xen sizing them and copying them in.
    Guard against this by re-checking the copyied in data for consistency
    with the initial sizing. At the same time also check that the actual
    copy-in is in fact successful, and switch to the lighter weight non-
    checking flavor of the function.
    
    Reported-by: Ilja Van Sprundel <ivansprundel@xxxxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>
    master commit: ad38db5852f0e30d90c93c6a62b754f2861549e0
    master date: 2020-02-06 09:51:17 +0100
---
 xen/common/efi/boot.c    | 10 ----------
 xen/common/efi/efi.h     |  2 ++
 xen/common/efi/runtime.c | 27 ++++++++++++++++++++++++---
 3 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index a1cd6c5e45..acd0b9968b 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -283,16 +283,6 @@ static int __init wstrncmp(const CHAR16 *s1, const CHAR16 
*s2, UINTN n)
     return n ? *s1 - *s2 : 0;
 }
 
-static const CHAR16 *__init wmemchr(const CHAR16 *s, CHAR16 c, UINTN n)
-{
-    while ( n && *s != c )
-    {
-        --n;
-        ++s;
-    }
-    return n ? s : NULL;
-}
-
 static CHAR16 *__init s2w(union string *str)
 {
     const char *s = str->s;
diff --git a/xen/common/efi/efi.h b/xen/common/efi/efi.h
index 6b9c56ead1..2e38d05f3d 100644
--- a/xen/common/efi/efi.h
+++ b/xen/common/efi/efi.h
@@ -39,3 +39,5 @@ extern UINT64 efi_boot_max_var_store_size, 
efi_boot_remain_var_store_size,
 
 extern UINT64 efi_apple_properties_addr;
 extern UINTN efi_apple_properties_len;
+
+const CHAR16 *wmemchr(const CHAR16 *s, CHAR16 c, UINTN n);
diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c
index 3d118d571d..a74f2a9d09 100644
--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -194,7 +194,18 @@ void efi_reset_system(bool warm)
 }
 
 #endif /* CONFIG_ARM */
-#endif
+
+const CHAR16 *wmemchr(const CHAR16 *s, CHAR16 c, UINTN n)
+{
+    while ( n && *s != c )
+    {
+        --n;
+        ++s;
+    }
+    return n ? s : NULL;
+}
+
+#endif /* COMPAT */
 
 #ifndef CONFIG_ARM /* TODO - disabled until implemented on ARM */
 int efi_get_info(uint32_t idx, union xenpf_efi_info *info)
@@ -468,7 +479,12 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         name = xmalloc_array(CHAR16, ++len);
         if ( !name )
            return -ENOMEM;
-        __copy_from_guest(name, op->u.get_variable.name, len);
+        if ( __copy_from_guest(name, op->u.get_variable.name, len) ||
+             wmemchr(name, 0, len) != name + len - 1 )
+        {
+            xfree(name);
+            return -EIO;
+        }
 
         size = op->u.get_variable.size;
         if ( size )
@@ -516,7 +532,12 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         name = xmalloc_array(CHAR16, ++len);
         if ( !name )
            return -ENOMEM;
-        __copy_from_guest(name, op->u.set_variable.name, len);
+        if ( __copy_from_guest(name, op->u.set_variable.name, len) ||
+             wmemchr(name, 0, len) != name + len - 1 )
+        {
+            xfree(name);
+            return -EIO;
+        }
 
         data = xmalloc_bytes(op->u.set_variable.size);
         if ( !data )
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.12

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