linux-kernel - Re: [PATCH v2 4/7] kvm/mips: rework guest entry logic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Yeqqle7lERyreSLi@FVFF77S0Q05N>
Date:   Fri, 21 Jan 2022 12:44:05 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, aleksandar.qemu.devel@...il.com,
        alexandru.elisei@....com, anup.patel@....com,
        aou@...s.berkeley.edu, atish.patra@....com,
        borntraeger@...ux.ibm.com, bp@...en8.de, catalin.marinas@....com,
        chenhuacai@...nel.org, dave.hansen@...ux.intel.com,
        frankja@...ux.ibm.com, frederic@...nel.org, gor@...ux.ibm.com,
        hca@...ux.ibm.com, james.morse@....com, jmattson@...gle.com,
        joro@...tes.org, luto@...nel.org, maz@...nel.org, mingo@...hat.com,
        mpe@...erman.id.au, nsaenzju@...hat.com, palmer@...belt.com,
        paulmck@...nel.org, paul.walmsley@...ive.com, peterz@...radead.org,
        seanjc@...gle.com, suzuki.poulose@....com, svens@...ux.ibm.com,
        tglx@...utronix.de, tsbogend@...ha.franken.de, vkuznets@...hat.com,
        wanpengli@...cent.com, will@...nel.org
Subject: Re: [PATCH v2 4/7] kvm/mips: rework guest entry logic

On Thu, Jan 20, 2022 at 06:29:25PM +0100, Paolo Bonzini wrote:
> On 1/20/22 18:15, Mark Rutland wrote:
> > As above, we'll also need the guest_state_{enter,exit}() calls
> > surrounding this (e.g. before that local_irq_enable() at the start of
> > kvm_mips_handle_exit(),
> 
> Oh, indeed.  And there is also an interrupt-enabled area similar to s390's,
> in both vcpu_run and the exception handler entry point (which falls through
> to the exit handler created by kvm_mips_build_exit).  For example:
> 
>         /* Setup status register for running guest in UM */
>         uasm_i_ori(&p, V1, V1, ST0_EXL | KSU_USER | ST0_IE);
>         UASM_i_LA(&p, AT, ~(ST0_CU0 | ST0_MX | ST0_SX | ST0_UX));
>         uasm_i_and(&p, V1, V1, AT);
>         uasm_i_mtc0(&p, V1, C0_STATUS);
>         uasm_i_ehb(&p);
> 
> I'd rather get rid altogether of the EQS for MIPS.

Ok; I'm not immediately sure how to do that without invasive changes around the
context tracking bits.

Did you have a specific approach in mind, or was that just a general statement?

> > and that needs to happen in noinstr code, etc.
> 
> There are bigger problems with instrumentation, because the
> runtime-generated code as far as I can tell is not noinstr.

The generated sequences themselves are not a problem -- they're not
compiler-instrumented, and kprobes will reject them since they live in a
kzalloc()'d buffer which is outside of kernel text.

Those call tlbmiss_handler_setup_pgd(), but that itself is runtime-generated,
and AFAICT doesn't call anything. It is placed within the kernel text, but it
could be blacklisted from kprobes.

Have I missed something there?

Thanks,
Mark.