On Thu, 2017-08-31 at 21:38 +0200, Borislav Petkov wrote: > On Fri, Aug 18, 2017 at 05:27:47PM -0700, Ricardo Neri wrote: > > Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software > > Developer's Manual volume 2A states that when ModRM.mod !=11b and > > ModRM.rm = 100b indexed register-indirect addressing is used. In other > > words, a SIB byte follows the ModRM byte. In the specific case of > > SIB.index = 100b, the scale*index portion of the computation of the > > effective address is null. To signal callers of this particular situation, > > get_reg_offset() can return -EDOM (-EINVAL continues to indicate that an > > error when decoding the SIB byte). > > > > An example of this situation can be the following instruction: > > > > 8b 4c 23 80 mov -0x80(%rbx,%riz,1),%rcx > > ModRM: 0x4c [mod:1b][reg:1b][rm:100b] > > SIB: 0x23 [scale:0b][index:100b][base:11b] > > Displacement: 0x80 (1-byte, as per ModRM.mod = 1b) > > > > The %riz 'register' indicates a null index. > > > > In long mode, a REX prefix may be used. When a REX prefix is present, > > REX.X adds a fourth bit to the register selection of SIB.index. This gives > > the ability to refer to all the 16 general purpose registers. When REX.X is > > 1b and SIB.index is 100b, the index is indicated in %r12. In our example, > > this would look like: > > > > 42 8b 4c 23 80 mov -0x80(%rbx,%r12,1),%rcx > > REX: 0x42 [W:0b][R:0b][X:1b][B:0b] > > ModRM: 0x4c [mod:1b][reg:1b][rm:100b] > > SIB: 0x23 [scale:0b][.X: 1b, index:100b][.B:0b, base:11b] > > Displacement: 0x80 (1-byte, as per ModRM.mod = 1b) > > > > %r12 is a valid register to use in the scale*index part of the effective > > address computation. > > > > Cc: Borislav Petkov <b...@suse.de> > > Cc: Andy Lutomirski <l...@kernel.org> > > Cc: Dave Hansen <dave.han...@linux.intel.com> > > Cc: Adam Buchbinder <adam.buchbin...@gmail.com> > > Cc: Colin Ian King <colin.k...@canonical.com> > > Cc: Lorenzo Stoakes <lstoa...@gmail.com> > > Cc: Qiaowei Ren <qiaowei....@intel.com> > > Cc: Peter Zijlstra <pet...@infradead.org> > > Cc: Nathan Howard <liverl...@gmail.com> > > Cc: Adan Hawthorn <adanhawth...@gmail.com> > > Cc: Joe Perches <j...@perches.com> > > Cc: Ravi V. Shankar <ravi.v.shan...@intel.com> > > Cc: x...@kernel.org > > Signed-off-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com> > > --- > > arch/x86/mm/mpx.c | 22 ++++++++++++++++++++-- > > 1 file changed, 20 insertions(+), 2 deletions(-) > > Reviewed-by: Borislav Petkov <b...@suse.de>
Thanks for your review!
