On Thu, Apr 02, 2020 at 06:03:57AM +0200, KP Singh wrote:
> On 01-Apr 17:09, Alexei Starovoitov wrote:
> > On Sat, Mar 28, 2020 at 5:44 PM KP Singh <kpsingh@xxxxxxxxxxxx> wrote:
> > > +int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
> > > + unsigned long reqprot, unsigned long prot, int ret)
> > > +{
> > > + if (ret != 0)
> > > + return ret;
> > > +
> > > + __u32 pid = bpf_get_current_pid_tgid() >> 32;
> > > + int is_heap = 0;
> > > +
> > > + is_heap = (vma->vm_start >= vma->vm_mm->start_brk &&
> > > + vma->vm_end <= vma->vm_mm->brk);
> >
> > This test fails for me.
>
> Trying this from bpf/master:
>
> b9258a2cece4 ("slcan: Don't transmit uninitialized stack data in padding")
>
> also from bpf-next/master:
>
> 1a323ea5356e ("x86: get rid of 'errret' argument to __get_user_xyz() macross")
>
> and I am unable to reproduce the failure (the output when using bpf/master):
..
>
> Also, I am wondering if this happens just in the BPF program or also
> in the kernel as the other variable I can think of is the compiled
> bpf program itself which might be reading a different value thinking
> it's vm->vma_start, possible something to do with BTF / CO RE due to a
> compiler bug:
I don't think it's anything to do with clang/btf or core.
I think that condition is simply incorrect.
I've added:
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 311c0dadf71c..16ae0ada34ba 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -577,6 +577,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
goto out;
}
+ printk("start %llx %llx\n", vma->vm_start, vma->vm_mm->start_brk);
error = security_file_mprotect(vma, reqprot, prot);
and see exactly the same values as bpf side (at least it was nice to see
that all CO-RE logic is working as expected :))
[ 24.787442] start 523000 39b9000
I think it has something to do with the way test_progs is linked.
But the problem is in condition itself.
I suspect you copy-pasted it from selinux_file_mprotect() ?
I think it's incorrect there as well.
Did we just discover a way to side step selinux protection?
Try objdump -h test_progs|grep bss
the number I see in vma->vm_start is the beginning of .bss rounded to page boundary.
I wonder where your 55dc6e8df000 is coming from.
