On Thu, Sep 24, 2020 at 01:47:47AM +0200, Jann Horn wrote: > On Thu, Sep 24, 2020 at 1:29 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > This emulates absolutely the most basic seccomp filters to figure out > > if they will always give the same results for a given arch/nr combo. > > > > Nearly all seccomp filters are built from the following ops: > > > > BPF_LD | BPF_W | BPF_ABS > > BPF_JMP | BPF_JEQ | BPF_K > > BPF_JMP | BPF_JGE | BPF_K > > BPF_JMP | BPF_JGT | BPF_K > > BPF_JMP | BPF_JSET | BPF_K > > BPF_JMP | BPF_JA > > BPF_RET | BPF_K > > > > These are now emulated to check for accesses beyond seccomp_data::arch > > or unknown instructions. > > > > Not yet implemented are: > > > > BPF_ALU | BPF_AND (generated by libseccomp and Chrome) > > BPF_AND is normally only used on syscall arguments, not on the syscall > number or the architecture, right? And when a syscall argument is > loaded, we abort execution anyway. So I think there is no need to > implement those? Is that right? I can't actually tell what libseccomp is doing with ALU|AND. It looks like it's using it for building jump lists? Paul, Tom, under what cases does libseccomp emit ALU|AND into filters? > > Suggested-by: Jann Horn <jannh@xxxxxxxxxx> > > Link: https://lore.kernel.org/lkml/CAG48ez1p=dR_2ikKq=xVxkoGg0fYpTBpkhJSv1w-6BG=76PAvw@xxxxxxxxxxxxxx/ > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > kernel/seccomp.c | 82 ++++++++++++++++++++++++++++++++++++++++++++--- > > net/core/filter.c | 3 +- > > 2 files changed, 79 insertions(+), 6 deletions(-) > > > > diff --git a/kernel/seccomp.c b/kernel/seccomp.c > > index 111a238bc532..9921f6f39d12 100644 > > --- a/kernel/seccomp.c > > +++ b/kernel/seccomp.c > > @@ -610,7 +610,12 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) > > { > > struct seccomp_filter *sfilter; > > int ret; > > - const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE); > > + const bool save_orig = > > +#if defined(CONFIG_CHECKPOINT_RESTORE) || defined(SECCOMP_ARCH) > > + true; > > +#else > > + false; > > +#endif > > You could probably write this as something like: > > const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) || > __is_defined(SECCOMP_ARCH); Ah! Thank you. I went looking for __is_defined() and failed. :) > > [...] > > diff --git a/net/core/filter.c b/net/core/filter.c > [...] > > -static void bpf_release_orig_filter(struct bpf_prog *fp) > > +void bpf_release_orig_filter(struct bpf_prog *fp) > > { > > struct sock_fprog_kern *fprog = fp->orig_prog; > > > > @@ -1154,6 +1154,7 @@ static void bpf_release_orig_filter(struct bpf_prog *fp) > > kfree(fprog); > > } > > } > > +EXPORT_SYMBOL_GPL(bpf_release_orig_filter); > > If this change really belongs into this patch (which I don't think it > does), please describe why in the commit message. Yup, more cruft I failed to remove. -- Kees Cook
