• Daniel Borkmann's avatar
    bpf: Add probe_read_{user, kernel} and probe_read_{user, kernel}_str helpers · 6ae08ae3
    Daniel Borkmann authored
    The current bpf_probe_read() and bpf_probe_read_str() helpers are broken
    in that they assume they can be used for probing memory access for kernel
    space addresses /as well as/ user space addresses.
    
    However, plain use of probe_kernel_read() for both cases will attempt to
    always access kernel space address space given access is performed under
    KERNEL_DS and some archs in-fact have overlapping address spaces where a
    kernel pointer and user pointer would have the /same/ address value and
    therefore accessing application memory via bpf_probe_read{,_str}() would
    read garbage values.
    
    Lets fix BPF side by making use of recently added 3d708182 ("uaccess:
    Add non-pagefault user-space read functions"). Unfortunately, the only way
    to fix this status quo is to add dedicated bpf_probe_read_{user,kernel}()
    and bpf_probe_read_{user,kernel}_str() helpers. The bpf_probe_read{,_str}()
    helpers are kept as-is to retain their current behavior.
    
    The two *_user() variants attempt the access always under USER_DS set, the
    two *_kernel() variants will -EFAULT when accessing user memory if the
    underlying architecture has non-overlapping address ranges, also avoiding
    throwing the kernel warning via 00c42373 ("x86-64: add warning for
    non-canonical user access address dereferences").
    
    Fixes: a5e8c070 ("bpf: add bpf_probe_read_str helper")
    Fixes: 2541517c
    
     ("tracing, perf: Implement BPF programs attached to kprobes")
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
    Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
    Link: https://lore.kernel.org/bpf/796ee46e948bc808d54891a1108435f8652c6ca4.1572649915.git.daniel@iogearbox.net
    6ae08ae3
bpf.h 138 KB