Re: [PATCH v5 00/12] Add CET shadow stack support

[Luis Machado <luis.machado@arm.com>]

Hi Christina,

On 7/11/25 14:54, Schimpe, Christina wrote:
> Hi Luis,
> 
> Thanks a lot for your testing efforts and spotting this.
> That's interesting, I just double checked and am not able to reproduce. Would you mind sharing a couple of details, e.g the kernel version? I assume that your cpu has CET shadow stack support since the register appears as "unavailable".

I'm running Ubuntu 24.04 on 6.8.0-63-generic.

CPU is Intel(R) Core(TM) Ultra 7 165U, with these features:

    Flags:                fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge m
                          ca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 s
                          s ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc 
                          art arch_perfmon pebs bts rep_good nopl xtopology nons
                          top_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq 
                          dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma c
                          x16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt t
                          sc_deadline_timer aes xsave avx f16c rdrand lahf_lm ab
                          m 3dnowprefetch cpuid_fault epb intel_ppin ssbd ibrs i
                          bpb stibp ibrs_enhanced tpr_shadow flexpriority ept vp
                          id ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms
                           invpcid rdseed adx smap clflushopt clwb intel_pt sha_
                          ni xsaveopt xsavec xgetbv1 xsaves split_lock_detect us
                          er_shstk avx_vnni dtherm ida arat pln pts hwp hwp_noti
                          fy hwp_act_window hwp_epp hwp_pkg_req hfi vnmi umip pk
                          u ospke waitpkg gfni vaes vpclmulqdq tme rdpid bus_loc
                          k_detect movdiri movdir64b fsrm md_clear serialize pco
                          nfig arch_lbr ibt flush_l1d arch_capabilities


So slightly older than yours. Anything else I can share that would help?

> 
> For me the shadow stack register is available in the corefile (ubuntu with linux kernel 6.13). 
> 
> (gdb) PASS: gdb.base/gcore.exp: where in corefile
> info registers^M
> rax            0x0                 0^M
> [...]
> k7             0x0                 0^M
> pl3_ssp        <unavailable>^M
> fs_base        0x7ffff7fae740      140737353803584^M
> gs_base        0x0                 0^M
> (gdb) PASS: gdb.base/gcore.exp: corefile restored general registers
> 
> Christina
> 
>> -----Original Message-----
>> From: Luis Machado <luis.machado@arm.com>
>> Sent: Friday, July 11, 2025 12:37 PM
>> To: Schimpe, Christina <christina.schimpe@intel.com>; gdb-
>> patches@sourceware.org
>> Cc: thiago.bauermann@linaro.org
>> Subject: Re: [PATCH v5 00/12] Add CET shadow stack support
>>
>> Hi Christina,
>>
>> I went through v5 and I have no further comments.
>>
>> I did try running the testsuite on my local x86-64 machine and noticed a
>> couple additional failures for native gdb testing.
>>
>> FAIL: gdb.base/gcore.exp: corefile restored general registers
>> FAIL: gdb.base/gcore.exp: corefile restored all registers
>>
>> Have you seen those? The problem seems to be that the pl3_ssp register is
>> showing up in a live session, but not in the core file.
>>
>> pl3_ssp        <unavailable>
>>
>> On 6/28/25 09:27, Christina Schimpe wrote:
>>> Hi all,
>>>
>>> this is my v5 of the series to add amd64 shadow stack support to GDB on
>> linux.
>>> It addresses the feedback of Luis.
>>>
>>> v4 can be found here:
>>> https://sourceware.org/pipermail/gdb-patches/2025-June/218744.html
>>>
>>> Changes since v4:
>>> - Improve some comments.
>>> - Change the test in "gdb: amd64 linux coredump support with shadow
>>>   stack." to also test core file generated by the linux kernel.  This
>>>   requires changes for the core_find procedure to save program output,
>>>   that have been implemented by Thiago already, so we include this part
>>>   of the patch in this series: "gdb, testsuite: Extend core_find procedure
>>>   to save program output.".  The test is now very similar to the test
>>>   implemented for Guarded Control Stack corefiles.  Thanks to Thiago for
>>>   providing the input here!
>>>
>>> I am looking forward to your feedback!
>>>
>>> Regards,
>>>
>>> Christina
>>>
>>> Christina Schimpe (12):
>>>   gdb, testsuite: Extend core_find procedure to save program output.
>>>   gdbserver: Add optional runtime register set type.
>>>   gdbserver: Add assert in x86_linux_read_description.
>>>   gdb: Sync up x86-gcc-cpuid.h with cpuid.h from gcc 14 branch.
>>>   gdb, gdbserver: Use xstate_bv for target description creation on x86.
>>>   gdb, gdbserver: Add support of Intel shadow stack pointer register.
>>>   gdb: amd64 linux coredump support with shadow stack.
>>>   gdb: Handle shadow stack pointer register unwinding for amd64 linux.
>>>   gdb, gdbarch: Enable inferior calls for shadow stack support.
>>>   gdb: Implement amd64 linux shadow stack support for inferior calls.
>>>   gdb, gdbarch: Introduce gdbarch method to get the shadow stack
>>>     pointer.
>>>   gdb: Enable displaced stepping with shadow stack on amd64 linux.
>>>
>>>  gdb/NEWS                                      |   6 +
>>>  gdb/amd64-linux-nat.c                         |  17 ++
>>>  gdb/amd64-linux-tdep.c                        | 218 +++++++++++++++++-
>>>  gdb/amd64-tdep.c                              |  35 ++-
>>>  gdb/amd64-tdep.h                              |   9 +-
>>>  gdb/arch-utils.c                              |  10 +
>>>  gdb/arch-utils.h                              |   5 +
>>>  gdb/arch/amd64-linux-tdesc.c                  |  33 +--
>>>  gdb/arch/amd64-linux-tdesc.h                  |   7 +-
>>>  gdb/arch/amd64.c                              |  25 +-
>>>  gdb/arch/amd64.h                              |  10 +-
>>>  gdb/arch/i386-linux-tdesc.c                   |  29 +--
>>>  gdb/arch/i386-linux-tdesc.h                   |   5 +-
>>>  gdb/arch/i386.c                               |  19 +-
>>>  gdb/arch/i386.h                               |   8 +-
>>>  gdb/arch/x86-linux-tdesc-features.c           |  60 ++---
>>>  gdb/arch/x86-linux-tdesc-features.h           |  25 +-
>>>  gdb/doc/gdb.texinfo                           |  42 ++++
>>>  gdb/features/Makefile                         |   2 +
>>>  gdb/features/i386/32bit-ssp.c                 |  14 ++
>>>  gdb/features/i386/32bit-ssp.xml               |  11 +
>>>  gdb/features/i386/64bit-ssp.c                 |  14 ++
>>>  gdb/features/i386/64bit-ssp.xml               |  11 +
>>>  gdb/gdbarch-gen.c                             |  54 +++++
>>>  gdb/gdbarch-gen.h                             |  24 ++
>>>  gdb/gdbarch_components.py                     |  31 +++
>>>  gdb/i386-tdep.c                               |  51 +++-
>>>  gdb/i386-tdep.h                               |  11 +-
>>>  gdb/infcall.c                                 |  14 +-
>>>  gdb/linux-tdep.c                              |  47 ++++
>>>  gdb/linux-tdep.h                              |   7 +
>>>  gdb/nat/x86-gcc-cpuid.h                       | 153 +++++++++---
>>>  gdb/nat/x86-linux-tdesc.c                     |  20 +-
>>>  gdb/nat/x86-linux-tdesc.h                     |   7 +-
>>>  gdb/nat/x86-linux.c                           |  57 +++++
>>>  gdb/nat/x86-linux.h                           |   4 +
>>>  .../gdb.arch/amd64-shadow-stack-cmds.exp      | 141 +++++++++++
>>>  .../gdb.arch/amd64-shadow-stack-corefile.c    |  42 ++++
>>>  .../gdb.arch/amd64-shadow-stack-corefile.exp  | 110 +++++++++
>>> .../gdb.arch/amd64-shadow-stack-disp-step.exp |  92 ++++++++
>>>  gdb/testsuite/gdb.arch/amd64-shadow-stack.c   |  35 +++
>>>  gdb/testsuite/gdb.arch/amd64-ssp.exp          |  50 ++++
>>>  .../gdb.base/inline-frame-cycle-unwind.py     |   4 +
>>>  gdb/testsuite/lib/gdb.exp                     |  80 ++++++-
>>>  gdb/x86-linux-nat.c                           |  50 +++-
>>>  gdb/x86-linux-nat.h                           |  11 +
>>>  gdb/x86-tdep.c                                |  21 ++
>>>  gdb/x86-tdep.h                                |   9 +
>>>  gdbserver/i387-fp.cc                          |  40 ++--
>>>  gdbserver/linux-amd64-ipa.cc                  |  10 +-
>>>  gdbserver/linux-i386-ipa.cc                   |   6 +-
>>>  gdbserver/linux-low.cc                        |  50 ++--
>>>  gdbserver/linux-low.h                         |   7 +-
>>>  gdbserver/linux-x86-low.cc                    |  44 +++-
>>>  gdbsupport/x86-xstate.h                       |   7 +-
>>>  55 files changed, 1687 insertions(+), 217 deletions(-)  create mode
>>> 100644 gdb/features/i386/32bit-ssp.c  create mode 100644
>>> gdb/features/i386/32bit-ssp.xml  create mode 100644
>>> gdb/features/i386/64bit-ssp.c  create mode 100644
>>> gdb/features/i386/64bit-ssp.xml  create mode 100644
>>> gdb/testsuite/gdb.arch/amd64-shadow-stack-cmds.exp
>>>  create mode 100644
>>> gdb/testsuite/gdb.arch/amd64-shadow-stack-corefile.c
>>>  create mode 100644
>>> gdb/testsuite/gdb.arch/amd64-shadow-stack-corefile.exp
>>>  create mode 100644
>>> gdb/testsuite/gdb.arch/amd64-shadow-stack-disp-step.exp
>>>  create mode 100644 gdb/testsuite/gdb.arch/amd64-shadow-stack.c
>>>  create mode 100644 gdb/testsuite/gdb.arch/amd64-ssp.exp
>>>
> 
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