[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 14:39, 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; > + } > + } Andrew, looking at this code I really wonder what benefit you request to move this further is going to have. Afaict no matter where we put it, it'll be an #ifdef around each of the two accesses to cr4_pv32_mask when we make that variable CONFIG_PV32-only. > --- a/xen/arch/x86/include/asm/setup.h > +++ b/xen/arch/x86/include/asm/setup.h > @@ -64,6 +64,8 @@ extern bool opt_dom0_verbose; > extern bool opt_dom0_cpuid_faulting; > extern bool opt_dom0_msr_relaxed; > > +extern unsigned long cr4_pv32_mask; With this ... > --- a/xen/arch/x86/setup.c > +++ b/xen/arch/x86/setup.c > @@ -80,7 +80,7 @@ int8_t __initdata opt_probe_port_aliases = -1; > boolean_param("probe-port-aliases", opt_probe_port_aliases); > > /* Only used in asm code and within this source file */ > -unsigned long asmlinkage __read_mostly cr4_pv32_mask; > +unsigned long asmlinkage __ro_after_init cr4_pv32_mask; ... both the comment and the asmlinkage become stale now. Jan
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