@@ -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]);
}
/*
__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> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> Tested-by: Mingwei Zhang <mizhang@google.com> Cc: x86@kernel.org Cc: linux-kernel@vger.kernel.org Link: https://lore.kernel.org/kvm/20230221163655.920289-2-mizhang@google.com/ --- Thanks, Mingwei for detecting the issue and Thomas for explaining the problem with the well-written description. The background and problem sections in this changelog came from his write-up. I acknowledge that Mingwei's patch (in the link above) can solve the problem. But, I would rather propose this approach as it simplifies the code which is considered good in this sensitive copy function. This mostly zeroed init_fpstate is still useful, e.g., when copying the init state between buffers with the same format -- like in fpu_clone(). But, this case between different XSAVE formats looks a bit different than that. --- arch/x86/kernel/fpu/xstate.c | 30 ++++++++++++++---------------- 1 file changed, 14 insertions(+), 16 deletions(-)