On Fri, Nov 18, 2022 at 3:47 AM Christophe Leroy <christophe.leroy@xxxxxxxxxx> wrote: > > > > Le 18/11/2022 à 10:39, Hari Bathini a écrit : > > > > > > On 18/11/22 2:21 pm, Christophe Leroy wrote: >>>>> > >>>>> I had the same config but hit this problem: > >>>>> > >>>>> # echo 1 > /proc/sys/net/core/bpf_jit_enable; modprobe test_bpf > >>>>> test_bpf: #0 TAX > >>>>> ------------[ cut here ]------------ > >>>>> WARNING: CPU: 0 PID: 96 at arch/powerpc/net/bpf_jit_comp.c:367 > >>>>> bpf_int_jit_compile+0x8a0/0x9f8 > >>>> > >>>> I get no such problem, on QEMU, and I checked the .config has: > >>> > >>>> CONFIG_STRICT_KERNEL_RWX=y > >>>> CONFIG_STRICT_MODULE_RWX=y > >>> > >>> Yeah. That did the trick. > >> > >> Interesting. I guess we have to find out why it fails when those config > >> are missing. > >> > >> Maybe module code plays with RO and NX flags even if > >> CONFIG_STRICT_MODULE_RWX is not selected ? > > > > Need to look at the code closely but fwiw, observing same failure on > > 64-bit as well with !STRICT_RWX... > > The problem is in bpf_prog_pack_alloc() and in alloc_new_pack() : They > do set_memory_ro() and set_memory_x() without taking into account > CONFIG_STRICT_MODULE_RWX. > > When CONFIG_STRICT_MODULE_RWX is selected, powerpc module_alloc() > allocates PAGE_KERNEL memory, that is RW memory, and expects the user to > call do set_memory_ro() and set_memory_x(). > > But when CONFIG_STRICT_MODULE_RWX is not selected, powerpc > module_alloc() allocates PAGE_KERNEL_TEXT memory, that is RWX memory, > and expects to be able to always write into it. Ah, I see. x86_64 requires CONFIG_STRICT_MODULE_RWX, so this hasn't been a problem yet. Thanks, Song
