Messages in this thread | | | Subject | Re: [PATCH v14 01/26] Documentation/x86: Add CET description | From | "Yu, Yu-cheng" <> | Date | Fri, 6 Nov 2020 10:16:47 -0800 |
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On 11/6/2020 9:34 AM, Borislav Petkov wrote: > On Mon, Oct 12, 2020 at 08:38:25AM -0700, Yu-cheng Yu wrote: >> +[1] Overview >> +============ >> + >> +Control-flow Enforcement Technology (CET) is an Intel processor feature >> +that provides protection against return/jump-oriented programming (ROP) >> +attacks. It can be set up to protect both applications and the kernel. >> +Only user-mode protection is implemented in the 64-bit kernel, including >> +support for running legacy 32-bit applications. >> + >> +CET introduces Shadow Stack and Indirect Branch Tracking. Shadow stack is >> +a secondary stack allocated from memory and cannot be directly modified by >> +applications. When executing a CALL, the processor pushes the return > ^ > . .. instruction ... >
I will update it.
[...]
>> + >> +[2] Application Enabling >> +======================== >> + >> +An application's CET capability is marked in its ELF header and can be >> +verified from the following command output, in the NT_GNU_PROPERTY_TYPE_0 >> +field: >> + >> + readelf -n <application> > > Can be verified how? What does it say for a CET-enabled executable? Put > it here in the doc pls. >
readelf -n <application> | grep SHSTK properties: x86 feature: IBT, SHSTK
I will add this.
[...]
>> +[3] Backward Compatibility >> +========================== >> + >> +GLIBC provides a few tunables for backward compatibility. >> + >> +GLIBC_TUNABLES=glibc.tune.hwcaps=-SHSTK,-IBT >> + Turn off SHSTK/IBT for the current shell. > > For the current shell? How? > > You mean, you execute the kernel shell with that variable set? So you > set this variable in any executable's env which links with glibc in > order to disable CET? > > In any case, this needs clarification. >
In the current shell, if GLIBC_TUNABLES variable is set as such, applications started will have CET features disabled. I can put more details here, or maybe a reference to the GLIBC man pages.
Thanks, Yu-cheng
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