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

Luis Machado
2025-07-11T15:56:05Z

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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