Re: [PATCH] gold: Remove BND from 64-bit x86-64 IBT PLT

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Dec 8, 2022 at 8:12 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Tue, Dec 6, 2022 at 1:44 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > Since MPX support has been removed from x86-64 psABI, remove BND from
> > 64-bit IBT PLT by using 32-bit IBT PLT.
> >
> >         PR gold/29851
> >         * x86_64.cc (Output_data_plt_x86_64_ibt<32>::first_plt_entry):
> >         Renamed to ...
> >         (Output_data_plt_x86_64_ibt<size>::first_plt_entry): This.
> >         (Output_data_plt_x86_64_ibt<64>::first_plt_entry): Removed.
> >         (Output_data_plt_x86_64_ibt<size>::do_fill_first_plt_entry):
> >         Drop the size == 32 check.
> >         (Output_data_plt_x86_64_ibt<32>::plt_entry): Renamed to ...
> >         (Output_data_plt_x86_64_ibt<size>::plt_entry): This.
> >         (Output_data_plt_x86_64_ibt<64>::plt_entry): Removed.
> >         (Output_data_plt_x86_64_ibt<32>::aplt_entry): Renamed to ...
> >         (Output_data_plt_x86_64_ibt<size>::aplt_entry): This.
> >         (Output_data_plt_x86_64_ibt<64>::aplt_entry): Removed.
> >         (Output_data_plt_x86_64_ibt<size>::do_fill_plt_entry): Drop the
> >         size == 32 check.
> >         (Output_data_plt_x86_64_ibt<size>::fill_aplt_entry): Likewise.
> > ---
> >  gold/x86_64.cc | 57 ++++++++------------------------------------------
> >  1 file changed, 9 insertions(+), 48 deletions(-)
> >
> > diff --git a/gold/x86_64.cc b/gold/x86_64.cc
> > index 86b232a5e2d..83684b90fcf 100644
> > --- a/gold/x86_64.cc
> > +++ b/gold/x86_64.cc
> > @@ -2328,12 +2328,10 @@ Output_data_plt_x86_64_ibt<size>::set_final_data_size()
> >
> >  // The first entry in the IBT PLT.
> >
> > -template<>
> > +template<int size>
> >  const unsigned char
> > -Output_data_plt_x86_64_ibt<32>::first_plt_entry[plt_entry_size] =
> > +Output_data_plt_x86_64_ibt<size>::first_plt_entry[plt_entry_size] =
> >  {
> > -  // MPX isn't supported for x32, so we don't need the BND prefix.
> > -  // From AMD64 ABI Draft 0.98, page 76
> >    0xff, 0x35,           // pushq contents of memory address
> >    0, 0, 0, 0,           // replaced with address of .got + 8
> >    0xff, 0x25,           // jmp indirect
> > @@ -2341,18 +2339,6 @@ Output_data_plt_x86_64_ibt<32>::first_plt_entry[plt_entry_size] =
> >    0x90, 0x90, 0x90, 0x90 // noop (x4)
> >  };
> >
> > -template<>
> > -const unsigned char
> > -Output_data_plt_x86_64_ibt<64>::first_plt_entry[plt_entry_size] =
> > -{
> > -  // Use the BND prefix so that IBT is compatible with MPX.
> > -  0xff, 0x35,          // pushq contents of memory address
> > -  0, 0, 0, 0,          // replaced with address of .got + 8
> > -  0xf2, 0xff, 0x25,    // bnd jmp indirect
> > -  0, 0, 0, 0,          // replaced with address of .got + 16
> > -  0x0f, 0x1f, 0x00     // nop
> > -};
> > -
> >  template<int size>
> >  void
> >  Output_data_plt_x86_64_ibt<size>::do_fill_first_plt_entry(
> > @@ -2362,7 +2348,7 @@ Output_data_plt_x86_64_ibt<size>::do_fill_first_plt_entry(
> >  {
> >    // Offsets to the addresses needing relocation.
> >    const unsigned int roff1 = 2;
> > -  const unsigned int roff2 = (size == 32) ? 8 : 9;
> > +  const unsigned int roff2 = 8;
> >
> >    memcpy(pov, first_plt_entry, plt_entry_size);
> >    // We do a jmp relative to the PC at the end of this instruction.
> > @@ -2376,9 +2362,9 @@ Output_data_plt_x86_64_ibt<size>::do_fill_first_plt_entry(
> >
> >  // Subsequent entries in the IBT PLT.
> >
> > -template<>
> > +template<int size>
> >  const unsigned char
> > -Output_data_plt_x86_64_ibt<32>::plt_entry[plt_entry_size] =
> > +Output_data_plt_x86_64_ibt<size>::plt_entry[plt_entry_size] =
> >  {
> >    // From AMD64 ABI Draft 1.0-rc1, Chapter 13.
> >    0xf3, 0x0f, 0x1e, 0xfa,      // endbr64
> > @@ -2389,24 +2375,11 @@ Output_data_plt_x86_64_ibt<32>::plt_entry[plt_entry_size] =
> >    0x90, 0x90                   // nop
> >  };
> >
> > -template<>
> > -const unsigned char
> > -Output_data_plt_x86_64_ibt<64>::plt_entry[plt_entry_size] =
> > -{
> > -  // From AMD64 ABI Draft 1.0-rc1, Chapter 13.
> > -  0xf3, 0x0f, 0x1e, 0xfa,      // endbr64
> > -  0x68,                                // pushq immediate
> > -  0, 0, 0, 0,                  // replaced with offset into relocation table
> > -  0xf2, 0xe9,                  // bnd jmpq relative
> > -  0, 0, 0, 0,                  // replaced with offset to start of .plt
> > -  0x90                         // nop
> > -};
> > -
> >  // Entries in the IBT Additional PLT.
> >
> > -template<>
> > +template<int size>
> >  const unsigned char
> > -Output_data_plt_x86_64_ibt<32>::aplt_entry[aplt_entry_size] =
> > +Output_data_plt_x86_64_ibt<size>::aplt_entry[aplt_entry_size] =
> >  {
> >    // From AMD64 ABI Draft 1.0-rc1, Chapter 13.
> >    0xf3, 0x0f, 0x1e, 0xfa,      // endbr64
> > @@ -2416,18 +2389,6 @@ Output_data_plt_x86_64_ibt<32>::aplt_entry[aplt_entry_size] =
> >    0x90, 0x90                   // nop
> >  };
> >
> > -template<>
> > -const unsigned char
> > -Output_data_plt_x86_64_ibt<64>::aplt_entry[aplt_entry_size] =
> > -{
> > -  // From AMD64 ABI Draft 1.0-rc1, Chapter 13.
> > -  0xf3, 0x0f, 0x1e, 0xfa,      // endbr64
> > -  0xf2, 0xff, 0x25,            // bnd jmpq indirect
> > -  0, 0, 0, 0,                  // replaced with address of symbol in .got
> > -  0x0f, 0x1f, 0x04, 0x00,      // nop
> > -  0x90,                                // nop
> > -};
> > -
> >  template<int size>
> >  unsigned int
> >  Output_data_plt_x86_64_ibt<size>::do_fill_plt_entry(
> > @@ -2440,7 +2401,7 @@ Output_data_plt_x86_64_ibt<size>::do_fill_plt_entry(
> >  {
> >    // Offsets to the addresses needing relocation.
> >    const unsigned int roff1 = 5;
> > -  const unsigned int roff2 = (size == 32) ? 10 : 11;
> > +  const unsigned int roff2 = 10;
> >
> >    memcpy(pov, plt_entry, plt_entry_size);
> >    elfcpp::Swap_unaligned<32, false>::writeval(pov + roff1, plt_index);
> > @@ -2459,7 +2420,7 @@ Output_data_plt_x86_64_ibt<size>::fill_aplt_entry(
> >      unsigned int plt_index)
> >  {
> >    // Offset to the address needing relocation.
> > -  const unsigned int roff = (size == 32) ? 6 : 7;
> > +  const unsigned int roff = 6;
> >
> >    // Check PC-relative offset overflow in PLT entry.
> >    uint64_t plt_got_pcrel_offset = (got_address + got_offset
> > --
> > 2.38.1
> >
>
> Hi Cary,
>
> Is it OK for gold?
>
> Thanks.
>
> --
> H.J.

I am checking it in today.

-- 
H.J.