On Wed, Feb 3, 2021 at 9:07 AM Yonghong Song <yhs@xxxxxx> wrote: > > > > On 2/2/21 5:50 AM, Brendan Jackman wrote: > > When BPF_FETCH is set, atomic instructions load a value from memory > > into a register. The current verifier code first checks via > > check_mem_access whether we can access the memory, and then checks > > via check_reg_arg whether we can write into the register. > > > > For loads, check_reg_arg has the side-effect of marking the > > register's value as unkonwn, and check_mem_access has the side effect > > of propagating bounds from memory to the register. This currently only > > takes effect for stack memory. > > > > Therefore with the current order, bounds information is thrown away, > > but by simply reversing the order of check_reg_arg > > vs. check_mem_access, we can instead propagate bounds smartly. > > > > A simple test is added with an infinite loop that can only be proved > > unreachable if this propagation is present. This is implemented both > > with C and directly in test_verifier using assembly. > > > > Suggested-by: John Fastabend <john.fastabend@xxxxxxxxx> > > Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx> > > Ack with a nit below. Sorry it was already applied yesterday. patchbot just didn't send auto-reply.
