[tip:,x86/urgent] x86/fpu/xstate: Prevent false-positive warning in __copy_xstate_uabi_buf()
Commit Message
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: b15888840207c2bfe678dd1f68a32db54315e71f
Gitweb: https://git.kernel.org/tip/b15888840207c2bfe678dd1f68a32db54315e71f
Author: Chang S. Bae <chang.seok.bae@intel.com>
AuthorDate: Mon, 27 Feb 2023 13:05:03 -08:00
Committer: Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Wed, 22 Mar 2023 10:59:13 -07:00
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
---
arch/x86/kernel/fpu/xstate.c | 30 ++++++++++++++----------------
1 file changed, 14 insertions(+), 16 deletions(-)
@@ -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]);
}
/*