x86/fpu/xstate: Prevent false-positive warning in __copy_xstate_uabi_buf()

__copy_xstate_to_uabi_buf() copies either from the tasks XSAVE buffer
or from init_fpstate into the ptrace buffer. Dynamic features, like
XTILEDATA, have an all zeroes init state and are not saved in
init_fpstate, which means the corresponding bit is not set in the
xfeatures bitmap of the init_fpstate header.

But __copy_xstate_to_uabi_buf() retrieves addresses for both the tasks
xstate and init_fpstate unconditionally via __raw_xsave_addr().

So if the tasks XSAVE buffer has a dynamic feature set, then the
address retrieval for init_fpstate triggers the warning in
__raw_xsave_addr() which checks the feature bit in the init_fpstate
header.

Remove the address retrieval from init_fpstate for extended features.
They have an all zeroes init state so init_fpstate has zeros for them.
Then zeroing the user buffer for the init state is the same as copying
them from init_fpstate.

Fixes: 2308ee57d93d ("x86/fpu/amx: Enable the AMX feature in 64-bit mode")
Reported-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/kvm/20230221163655.920289-2-mizhang@google.com/
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/all/20230227210504.18520-2-chang.seok.bae%40intel.com
Cc: stable@vger.kernel.org

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 714166c..0bab497 100644 (file)
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1118,21 +1118,20 @@ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
        zerofrom = offsetof(struct xregs_state, extended_state_area);
 
        /*
-        * The ptrace buffer is in non-compacted XSAVE format.  In
-        * non-compacted format disabled features still occupy state space,
-        * but there is no state to copy from in the compacted
-        * init_fpstate. The gap tracking will zero these states.
-        */
-       mask = fpstate->user_xfeatures;
-
-       /*
-        * Dynamic features are not present in init_fpstate. When they are
-        * in an all zeros init state, remove those from 'mask' to zero
-        * those features in the user buffer instead of retrieving them
-        * from init_fpstate.
+        * This 'mask' indicates which states to copy from fpstate.
+        * Those extended states that are not present in fpstate are
+        * either disabled or initialized:
+        *
+        * In non-compacted format, disabled features still occupy
+        * state space but there is no state to copy from in the
+        * compacted init_fpstate. The gap tracking will zero these
+        * states.
+        *
+        * The extended features have an all zeroes init state. Thus,
+        * remove them from 'mask' to zero those features in the user
+        * buffer instead of retrieving them from init_fpstate.
         */
-       if (fpu_state_size_dynamic())
-               mask &= (header.xfeatures | xinit->header.xcomp_bv);
+       mask = header.xfeatures;
 
        for_each_extended_xfeature(i, mask) {
                /*
@@ -1151,9 +1150,8 @@ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
                        pkru.pkru = pkru_val;
                        membuf_write(&to, &pkru, sizeof(pkru));
                } else {
-                       copy_feature(header.xfeatures & BIT_ULL(i), &to,
+                       membuf_write(&to,
                                     __raw_xsave_addr(xsave, i),
-                                    __raw_xsave_addr(xinit, i),
                                     xstate_sizes[i]);
                }
                /*