On Fri, Apr 05, 2024 at 12:02:36PM +0100, Mark Rutland wrote: > On Thu, Apr 04, 2024 at 03:57:04PM -0700, Alexei Starovoitov wrote: > > On Wed, Apr 3, 2024 at 6:56 PM Andrew Morton <akpm@linux-foundationorg> wrote: > > > > > > On Mon, 01 Apr 2024 22:19:25 -0700 syzbot <syzbot+186522670e6722692d86@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > Hello, > > > > > > Thanks. Cc: bpf@xxxxxxxxxxxxxxx > > > > I suspect the issue is not on bpf side. > > Looks like the bug is somewhere in arm32 bits. > > copy_from_kernel_nofault() is called from lots of places. > > bpf is just one user that is easy for syzbot to fuzz. > > Interestingly arm defines copy_from_kernel_nofault_allowed() > > that should have filtered out user addresses. > > In this case ffffffe9 is probably a kernel address? > > It's at the end of the kernel range, and it's ERR_PTR(-EINVAL). > > 0xffffffe9 is -0x16, which is -22, which is -EINVAL. > > > But the kernel is doing a write? > > Which makes no sense, since copy_from_kernel_nofault is probe reading. > > It makes perfect sense; the read from 'src' happened, then the kernel tries to > write the result to 'dst', and that aligns with the disassembly in the report > below, which I beleive is: > > 8: e4942000 ldr r2, [r4], #0 <-- Read of 'src', fault fixup is elsewhere > c: e3530000 cmp r3, #0 > * 10: e5852000 str r2, [r5] <-- Write to 'dst' > > As above, it looks like 'dst' is ERR_PTR(-EINVAL). > > Are you certain that BPF is passing a sane value for 'dst'? Where does that > come from in the first place? It looks to me like it gets passed in from the BPF program, and the "type" for the argument is set to ARG_PTR_TO_UNINIT_MEM. What that means for validation purposes, I've no idea, I'm not a BPF hacker. Obviously, if BPF is allowing copy_from_kernel_nofault() to be passed an arbitary destination address, that would be a huge security hole. So I think BPF folk need to urgently state what checks are done on the destination value for _any_ function that BPF can call which writes to memory. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
