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.co... Cc: stable@vger.kernel.org --- arch/x86/kernel/fpu/xstate.c | 30 ++++++++++++++---------------- 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 714166c..0bab497 100644 --- 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]); } /*