[xen staging] efi: fix alignment of function parameters in compat mode

[patchbot@xxxxxxx]

commit be12fcca8b784e456df3adedbffe657d753c5ff9
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Nov 18 09:28:06 2021 +0100
Commit:     Ian Jackson <iwj@xxxxxxxxxxxxxx>
CommitDate: Fri Nov 19 17:01:24 2021 +0000

    efi: fix alignment of function parameters in compat mode
    
    Currently the max_store_size, remain_store_size and max_size in
    compat_pf_efi_runtime_call are 4 byte aligned, which makes clang
    13.0.0 complain with:
    
    In file included from compat.c:30:
    ./runtime.c:646:13: error: passing 4-byte aligned argument to 8-byte 
aligned parameter 2 of 'QueryVariableInfo' may result in an unaligned pointer 
access [-Werror,-Walign-mismatch]
                &op->u.query_variable_info.max_store_size,
                ^
    ./runtime.c:647:13: error: passing 4-byte aligned argument to 8-byte 
aligned parameter 3 of 'QueryVariableInfo' may result in an unaligned pointer 
access [-Werror,-Walign-mismatch]
                &op->u.query_variable_info.remain_store_size,
                ^
    ./runtime.c:648:13: error: passing 4-byte aligned argument to 8-byte 
aligned parameter 4 of 'QueryVariableInfo' may result in an unaligned pointer 
access [-Werror,-Walign-mismatch]
                &op->u.query_variable_info.max_size);
                ^
    Fix this by bouncing the variables on the stack in order for them to
    be 8 byte aligned.
    
    Note this could be done in a more selective manner to only apply to
    compat code calls, but given the overhead of making an EFI call doing
    an extra copy of 3 variables doesn't seem to warrant the special
    casing.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
    Reviewed-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
    Signed-off-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    
    ---
    Changes since v3:
     - Remove hard tabs.  Apply Jan's r-b as authorised in email.
    Changes since v2:
     - Adjust the commentary as per discussion.
    Changes since v1:
     - Copy back the results.
---
 xen/common/efi/runtime.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c
index 375b94229e..d2fdc28df3 100644
--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -607,6 +607,9 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
     break;
 
     case XEN_EFI_query_variable_info:
+    {
+        uint64_t max_store_size, remain_store_size, max_size;
+
         if ( op->misc & ~XEN_EFI_VARINFO_BOOT_SNAPSHOT )
             return -EINVAL;
 
@@ -638,16 +641,36 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
 
         if ( !efi_enabled(EFI_RS) || (efi_rs->Hdr.Revision >> 16) < 2 )
             return -EOPNOTSUPP;
+
+        /*
+         * Bounce the variables onto the stack to make them 8 byte aligned when
+         * called from the compat handler, as their placement in
+         * compat_pf_efi_runtime_call will make them 4 byte aligned instead and
+         * and compilers may validly complain.
+         *
+         * Note that while the function parameters are OUT only, copy the
+         * values here anyway just in case. This is done regardless of whether
+         * called from the compat handler or not, as it's not worth the extra
+         * logic to differentiate.
+         */
+        max_store_size = op->u.query_variable_info.max_store_size;
+        remain_store_size = op->u.query_variable_info.remain_store_size;
+        max_size = op->u.query_variable_info.max_size;
+
         state = efi_rs_enter();
         if ( !state.cr3 )
             return -EOPNOTSUPP;
         status = efi_rs->QueryVariableInfo(
-            op->u.query_variable_info.attr,
-            &op->u.query_variable_info.max_store_size,
-            &op->u.query_variable_info.remain_store_size,
-            &op->u.query_variable_info.max_size);
+            op->u.query_variable_info.attr, &max_store_size, 
&remain_store_size,
+            &max_size);
         efi_rs_leave(&state);
+
+        op->u.query_variable_info.max_store_size = max_store_size;
+        op->u.query_variable_info.remain_store_size = remain_store_size;
+        op->u.query_variable_info.max_size = max_size;
+
         break;
+    }
 
     case XEN_EFI_query_capsule_capabilities:
     case XEN_EFI_update_capsule:
--
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