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11/09/2025 23:03, Yang Shi wrote: >> Hi Ryan & Catalin, >> >> Any more concerns about this? > I've been trying to convince myself that your assertion that all users that set > the VM_FLUSH_RESET_PERMS also call set_memory_*() for the entire range that was > returned my vmalloc. I agree that if that is the contract and everyone is > following it, then there is no problem here. > > But I haven't been able to convince myself... > > Some examples (these might intersect with examples you previously raised): > > 1. bpf_dispatcher_change_prog() -> bpf_jit_alloc_exec() -> execmem_alloc() -> > sets VM_FLUSH_RESET_PERMS. But I don't see it calling set_memory_*() for rw_image. Yes, it doesn't call set_memory_*(). I spotted this in the earlier email. But it is actually RW, so it should be ok to miss the call. The later set_direct_map_invalid call in vfree() may fail, but set_direct_map_default call will set RW permission back. But I think it doesn't have to use execmem_alloc(), the plain vmalloc() should be good enough. > > 2. module_memory_alloc() -> execmem_alloc_rw() -> execmem_alloc() -> sets > VM_FLUSH_RESET_PERMS (note that execmem_force_rw() is nop for arm64). > set_memory_*() is not called until much later on in module_set_memory(). Another > error in the meantime could cause the memory to be vfreed before that point. IIUC, execmem_alloc_rw() is used to allocate memory for modules' text section and data section. The code will set mod->mem[type].is_rox according to the type of the section. It is true for text, false for data. Then set_memory_rox() will be called later if it is true *after* insns are copied to the memory. So it is still RW before that point. > > 3. When set_vm_flush_reset_perms() is set for the range, it is called before > set_memory_*() which might then fail to split prior to vfree. Yes, all call sites check the return value and bail out if set_memory_*() failed if I don't miss anything. > > But I guess as long as set_memory_*() is never successfully called for a > *sub-range* of the vmalloc'ed region, then for all of the above issues, the > memory must still be RW at vfree-time, so this issue should be benign... I think? Yes, it is true. > > In summary this all looks horribly fragile. But I *think* it works. It would be > good to clean it all up and have some clearly documented rules regardless. But I > think that could be a follow up series. Yeah, absolutely agreed. > >> Shall we move forward with v8? > Yes; Do you wnat me to post that or would you prefer to do it? I'm happy to do > it; there are a few other tidy ups in pageattr.c I want to make which I spotted. I actually just had v8 ready in my tree. I removed pageattr_pgd_entry and pageattr_pud_entry in pageattr.c and fixed pmd_leaf/pud_leaf as you suggested. Is it the cleanup you are supposed to do? And I also rebased it on top of Shijie's series (https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=bfbbb0d3215f) which has been picked up by Will. > >> We can include the >> fix to kprobes in v8 or I can send it separately, either is fine to me. > Post it on list, and I'll also incorporate into the series. I can include it in v8 series. > >> Hopefully we can make v6.18. > It's probably getting a bit late now. Anyway, I'll aim to get v8 out tomorrow or > Friday and we will see what Will thinks. Thank you. I can post v8 today. Thanks, Yang > > Thanks, > Ryan > >> Thanks, >> Yang >>