Re: [PATCH 3/3] s390/pci: Add function handle to RPCIT insn trace

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Wed, 2026-10-07 at 15:12 +0200, Gerd Bayer wrote:
> On Wed, 2026-10-07 at 11:17 +0000, sashiko-bot@kernel.org wrote:
> > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> > - [Medium] s390/pci: info leak of uninitialized struct padding in zpci_err_insn_rpcit
> > --
> > 
> > commit 9deafec98847a2a1de20826fbaa6431e1e3c973f
> > Author: Gerd Bayer <gbayer@linux.ibm.com>
> > 
> > s390/pci: Add function handle to RPCIT insn trace
> > 
> > In certain debug situations it would be helpful, if the insn trace for a
> > failing RPCIT would reveal the PCI function on which this was attempted.
> > 
> > Introduce a variant of zpci_err_insn_req() called zpci_err_insn_rpcit()
> > that accepts an IO virtual address and a range parameter together with
> > the req conveying the function handle. Switch zpci_refresh_trans() to
> > use that new error trace.
> > 
> > > diff --git a/arch/s390/pci/pci_insn.c b/arch/s390/pci/pci_insn.c
> > > index 053afb3e7a990..ae9ed4aa2ec9c 100644
> > > --- a/arch/s390/pci/pci_insn.c
> > > +++ b/arch/s390/pci/pci_insn.c
--- snip ---
> > 
> > [Severity: Medium]
> > Does this code leak uninitialized stack memory to the s390dbf debug trace
> > buffer?
> > 
> > According to the C standard, unnamed bit-fields do not participate in
> > designated initialization. The struct zpci_err_insn_data starts with:
> > 
> > struct zpci_err_insn_data {
> > 	u8 insn;
> > 	u8 cc;
> > 	u8 status;
> > 	u8: 8;
> > 	u32: 32;
> >     ...
> > 
> > Because the unnamed bit-fields are skipped by the designated initializer here,
> > up to 5 bytes of uninitialized kernel stack memory are left in the padding
> > of "data".
> > 
> > Since sizeof(data) (which is 32 bytes) is then passed to zpci_err_hex_level(),
> > could these indeterminate stack bytes be copied into the trace buffer on every
> > invocation of zpci_err_insn_rpcit()?
> 
> This is basically the same concern as with patch 1/3 - I'll replace the
> unnamed bit-fields with dummy members of appropriate size in a v2.

Same as for the other patch this sounds good to me and the rest of the
change looks good too. Having the function handle could come in handy.

Thanks,
Niklas