[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v5] x86/dom0: disable SMAP for PV domain building only
On 27.08.2024 15:51, Roger Pau Monné wrote: > On Tue, Aug 27, 2024 at 02:07:07PM +0100, Andrew Cooper wrote: >> On 27/08/2024 2:04 pm, Jan Beulich wrote: >>> On 27.08.2024 14:59, Andrew Cooper wrote: >>>> On 27/08/2024 1:39 pm, Roger Pau Monne wrote: >>>>> --- a/xen/arch/x86/dom0_build.c >>>>> +++ b/xen/arch/x86/dom0_build.c >>>>> @@ -612,7 +612,24 @@ int __init construct_dom0(struct domain *d, const >>>>> module_t *image, >>>>> if ( is_hvm_domain(d) ) >>>>> rc = dom0_construct_pvh(d, image, image_headroom, initrd, >>>>> cmdline); >>>>> else if ( is_pv_domain(d) ) >>>>> + { >>>>> + /* >>>>> + * Temporarily clear SMAP in CR4 to allow user-accesses in >>>>> + * construct_dom0(). This saves a large number of corner cases >>>>> + * interactions with copy_from_user(). >>>>> + */ >>>>> + if ( boot_cpu_has(X86_FEATURE_XEN_SMAP) ) >>>>> + { >>>>> + cr4_pv32_mask &= ~X86_CR4_SMAP; >>>>> + write_cr4(read_cr4() & ~X86_CR4_SMAP); >>>>> + } >>>>> rc = dom0_construct_pv(d, image, image_headroom, initrd, >>>>> cmdline); >>>>> + if ( boot_cpu_has(X86_FEATURE_XEN_SMAP) ) >>>>> + { >>>>> + write_cr4(read_cr4() | X86_CR4_SMAP); >>>>> + cr4_pv32_mask |= X86_CR4_SMAP; >>>>> + } >>>>> + } >>>> I hate to drag this on further still, but can this logic be move it into >>>> dom0_construct_pv() itself, rather than here? >>> Just to mention it: I'm fine with this in principle, as long as this won't >>> mean a pile of new goto-s in dom0_construct_pv(). If a new wrapper was >>> introduced (with the present function becoming static), I'd be okay. >> >> I'd be happy with that too. >> >> In fact, static helpers are probably best, seeing as we'll eventually >> need real #ifdefary around the cr4_pv32_mask accesses. > > Do you mean a static helper in dom0_build.c for enabling/disabling > SMAP? While that's how I understood Andrew's response, I'm not sure that'll buy us very much. They'll both be used just once, and hence the amount of #ifdef-ary is going to be the same as when the logic is kept in line. Jan
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