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

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__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: 2308ee57d9 ("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
This commit is contained in:
Chang S. Bae 2023-02-27 13:05:03 -08:00 committed by Dave Hansen
parent a3f547addc
commit b158888402
1 changed files with 14 additions and 16 deletions
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30
arch/x86/kernel/fpu/xstate.c
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@ -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.
* 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.
*/
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.
*/
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]);
}
/*