Messages in this thread | | | Date | Wed, 18 Aug 2021 14:03:29 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v9 11/26] x86/fpu/xstate: Update the XSTATE context copy function to support dynamic states |
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On Fri, Jul 30, 2021 at 07:59:42AM -0700, Chang S. Bae wrote: > ptrace() and signal return paths use XSTATE context copy functions. They > allow callers to read (or write) XSTATE values in the target's buffer. With > dynamic user states, a component's position in the buffer may vary and the > init fpstate is not always large enough to cover all the states. > > Adjust the helpers to find a component's offset correctly. Also, update the > copy loop in the ptrace read path to support dynamic states. > > Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> > Reviewed-by: Len Brown <len.brown@intel.com> > Cc: x86@kernel.org > Cc: linux-kernel@vger.kernel.org > --- > Changes from v5: > * Updated to ensure xstate_bv aligned with the target. > * Rewrote the xstate copy loop, for the ptrace() read path, in an open > code. > * Adjusted the changelog. > > Changes from v3: > * Cleaned up the code change with more comments. > * Removed 'no functional change' in the changelog. (Borislav Petkov) > > Changes from v2: > * Updated the changelog with task->fpu removed. (Borislav Petkov) > --- > arch/x86/kernel/fpu/xstate.c | 30 +++++++++++++++++++++++++----- > 1 file changed, 25 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c > index 98ab10e4da3b..3b56e7612c45 100644 > --- a/arch/x86/kernel/fpu/xstate.c > +++ b/arch/x86/kernel/fpu/xstate.c > @@ -1273,6 +1273,7 @@ void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk, > zerofrom = offsetof(struct xregs_state, extended_state_area); > > for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) { > + u64 mask = BIT_ULL(i); > /* > * The ptrace buffer is in non-compacted XSAVE format. > * In non-compacted format disabled features still occupy > @@ -1280,7 +1281,7 @@ void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk, > * compacted init_fpstate. The gap tracking will zero this > * later. > */ > - if (!(xfeatures_mask_uabi() & BIT_ULL(i))) > + if (!(xfeatures_mask_uabi() & mask)) > continue; > > /* > @@ -1300,10 +1301,24 @@ void copy_xstate_to_uabi_buf(struct membuf to, struct task_struct *tsk, > pkru.pkru = tsk->thread.pkru; > membuf_write(&to, &pkru, sizeof(pkru)); > } else {
So this chunk, the else branch starting here is begging to be a separate function.
> - copy_feature(header.xfeatures & BIT_ULL(i), &to, > - __raw_xsave_addr(&tsk->thread.fpu, i), > - __raw_xsave_addr(NULL, i), > - xstate_sizes[i]); > + unsigned int size = xstate_sizes[i]; > + void *from = NULL; > + > + /* > + * Copy the xstate if available. Otherwise, copy the > + * non-zero init states for legacy states (FP and > + * SSE) or fill zeros. > + */ > + > + if (header.xfeatures & mask) > + from = __raw_xsave_addr(&tsk->thread.fpu, i); > + else if (XFEATURE_MASK_FPSSE & mask)
The i loop variable above starts from FIRST_EXTENDED_XFEATURE - why is this XFEATURE_MASK_FPSSE check even here?
> + from = __raw_xsave_addr(NULL, i); > + > + if (from) > + membuf_write(&to, from, size); > + else > + membuf_zero(&to, size); > } > /* > * Keep track of the last copied state in the non-compacted > @@ -1345,6 +1360,8 @@ static int copy_uabi_to_xstate(struct fpu *fpu, const void *kbuf, > if (validate_user_xstate_header(&hdr)) > return -EINVAL; > > + hdr.xfeatures &= fpu->state_mask; > +
This hunk looks arbitrary here and wants to be together with the patch which adds ->state_mask.
> /* Validate MXCSR when any of the related features is in use */ > mask = XFEATURE_MASK_FP | XFEATURE_MASK_SSE | XFEATURE_MASK_YMM; > if (hdr.xfeatures & mask) { > @@ -1371,6 +1388,9 @@ static int copy_uabi_to_xstate(struct fpu *fpu, const void *kbuf, > if (hdr.xfeatures & mask) { > void *dst = __raw_xsave_addr(fpu, i); > > + if (!dst) > + continue; > + > offset = xstate_offsets[i]; > size = xstate_sizes[i];
I don't know where this hunk belongs to...
Maybe as a completely separate patch which fixes the case where __raw_xsave_addr() can in the very unlikely event return NULL...
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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