On 2023-05-12 09:36, Jon Turney wrote:
On 08/05/2023 04:12, Brian Inglis wrote:
cpuid 0x00000007:0 ecx:7 shstk Shadow Stack support & Windows
[20]20H1/[20]2004+
=> user_shstk User mode program Shadow Stack support
AMD SVM 0x8000000a:0 edx:25 vnmi virtual Non-Maskable Interrrupts
Sync AMD 0x80000008:0 ebx flags across two output locations
Thanks. I applied this.
Does this need applying to the 3.4 branch as well?
How many users with the latest models will worry about this before 3.5 release
about October, and may Cygwin have support by then?
---
winsup/cygwin/fhandler/proc.cc | 29 ++++++++++++++++++++++-------
+ /* cpuid 0x00000007 ecx & Windows [20]20H1/[20]2004+ */
+ if (maxf >= 0x00000007 && wincap.osname () >= "10.0"
+ && wincap.build_number () >= 19041)
+ {
+ cpuid (&unused, &unused, &features1, &unused, 0x00000007, 0);
+ ftcprint (features1, 7, "user_shstk"); /* "user shadow stack" */
+ }
+
This seems a little odd and maybe worthy of a comment, as surely the CPU has the
capability irrespective of the OS?
Yes, see the log comment documenting the shtsk feature and the Windows release
supporting the process feature, and the patch comment echoing that.
Intel 11th gen and AMD Zen3+ processor models both support the same Control-flow
Enforcement Technology CET and shstk cpuid and arch features, save areas, MSRs,
etc.
That is the (currently commented out in the patch) shstk feature, which is
detected by the Linux kernel but not reported by Linux cpuinfo, and not yet
fully supported in the kernel by the Intel CET Linux patches.
Whereas Linux cpuinfo does report "user_shstk", which depends on kernel,
process, compiler, library, and image support, which requires Windows from
[20]20H1/[20]2004+ enabling and setting up the supported variants of CET flagged
in one of the process image debug headers, and saving/restoring the shadow stack
pointer SSP register.
https://www.intel.com/content/www/us/en/developer/articles/technical/technical-look-control-flow-enforcement-technology.html
The current GCC supports -mshstk, but I don't know if there is yet any back end
support for variants of CET to be flagged in ELF or PE32+ process image debug
headers, or plans for newlib x86 or Cygwin startup support, and exception
handling?
--
Take care. Thanks, Brian Inglis Calgary, Alberta, Canada
La perfection est atteinte Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer but when there is no more to cut
-- Antoine de Saint-Exupéry
