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Fix attaching fentry/fexit/fmod_ret/lsm to modules #4159

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Fix attaching fentry/fexit/fmod_ret/lsm to modules #4159

wants to merge 3 commits into from

Commits on Dec 5, 2022

  1. kallsyms: add space-efficient lookup in one module 

    Until now, the only way to look up a symbol in kallsyms of a particular
module was using the "module_kallsyms_lookup_name" function with the
"module:symbol" string passed as a parameter. This syntax often requires
to build the parameter string on stack, needlessly wasting space.

This commit introduces function "kallsyms_lookup_name_in_module" which
takes the module and the symbol names as separate parameters and
therefore allows more space-efficient lookup.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
    Viktor Malik authored and Kernel Patches Daemon committed Dec 5, 2022
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  2. bpf: Fix attaching fentry/fexit/fmod_ret/lsm to modules 

    When attaching fentry/fexit/fmod_ret/lsm to a function located in a
module without specifying the target program, the verifier tries to find
the address to attach to in kallsyms. This is always done by searching
the entire kallsyms, not respecting the module in which the function is
located.

This approach causes an incorrect attachment address to be computed if
the function to attach to is shadowed by a function of the same name
located earlier in kallsyms.

Since the attachment must contain the BTF of the program to attach to,
we may extract the module name from it (if the attach target is a
module) and search for the function address in the correct module.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
Acked-by: Hao Luo <haoluo@google.com>
    Viktor Malik authored and Kernel Patches Daemon committed Dec 5, 2022
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  3. bpf/selftests: Test fentry attachment to shadowed functions 

    Adds a new test that tries to attach a program to fentry of two
functions of the same name, one located in vmlinux and the other in
bpf_testmod.

To avoid conflicts with existing tests, a new function
"bpf_fentry_shadow_test" was created both in vmlinux and in bpf_testmod.

The previous commit fixed a bug which caused this test to fail. The
verifier would always use the vmlinux function's address as the target
trampoline address, hence trying to attach two programs to the same
trampoline.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
    Viktor Malik authored and Kernel Patches Daemon committed Dec 5, 2022
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