Messages in this thread | | | Date | Fri, 17 May 2024 17:39:51 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH] x86/kvm/tdx: Save %rbp in TDX_MODULE_CALL |
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On Fri, May 17, 2024 at 04:08:03PM +0200, Juergen Gross wrote: > On 17.05.24 15:55, Kirill A. Shutemov wrote: > > On Fri, May 17, 2024 at 02:14:50PM +0200, Juergen Gross wrote: > > > While testing TDX host support patches, a crash of the host has been > > > observed a few instructions after doing a seamcall. Reason was a > > > clobbered %rbp (set to 0), which occurred in spite of the TDX module > > > offering the feature NOT to modify %rbp across TDX module calls. > > > > > > In order not having to build the host kernel with CONFIG_FRAME_POINTER, > > > save %rbp across a seamcall/tdcall. > > > > There's a feature in TDX module 1.5 that prevents RBP modification across > > TDH.VP.ENTER SEAMCALL. See NO_RBP_MOD in TDX Module 1.5 ABI spec. > > > > I think it has to be enabled for all TDs and TDX modules that don't > > support it need to be rejected. > > > > Yes, I know. I'm using the patch series: > > [PATCH v19 000/130] KVM TDX basic feature support > > which I think does exactly that (see setup_tdparams() and tdx_module_setup()).
Looks like the check is broken:
https://lore.kernel.org/all/46mh5hinsv5mup2x7jv4iu2floxmajo2igrxb3haru3cgjukbg@v44nspjozm4h/
> Nevertheless the clobbering happened, and saving/restoring %rbp made the > issue to go away. I suspect there is a path left still clobbering %rbp.
What is your TDX module version? My guess is that NOM_RBP_MOD is not supported by it and given that the check is broken nobody enforces it.
-- Kiryl Shutsemau / Kirill A. Shutemov
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