[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] xen/privcmd: allow fetching resource sizes
On 11/01/2021 22:09, boris.ostrovsky@xxxxxxxxxx wrote: > On 1/11/21 10:29 AM, Roger Pau Monne wrote: >> >> + xdata.domid = kdata.dom; >> + xdata.type = kdata.type; >> + xdata.id = kdata.id; >> + >> + if (!kdata.addr && !kdata.num) { > > I think we should not allow only one of them to be zero. If it's only > kdata.num then we will end up with pfns array set to ZERO_SIZE_PTR (which is > 0x10). We seem to be OK in that we are not derefencing pfns (either in kernel > or in hypervisor) if number of frames is zero but IMO we shouldn't be > tempting the fate. > > > (And if it's only kdata.addr then we will get a vma but I am not sure it will > do what we want.) Passing addr == 0 without num being 0 is already an error in Xen, and passing num == 0 without addr being 0 is bogus and will be an error by the time I'm finished fixing this. FWIW, the common usecase for non-trivial examples will be: xenforeignmem_resource_size(domid, type, id, &size); xenforeignmem_map_resource(domid, type, id, NULL, size, ...); which translates into: ioctl(MAP_RESOURCE, NULL, 0) => size mmap(NULL, size, ...) => ptr ioctl(MAP_RESOURCE, ptr, size) from the kernels point of view, and two hypercalls from Xen's point of view. The NULL's above are expected to be the common case for letting the kernel chose the vma, but ought to be filled in by the time the second ioctl() occurs. See https://lore.kernel.org/xen-devel/20200922182444.12350-1-andrew.cooper3@xxxxxxxxxx/T/#u for all the gory details. ~Andrew
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