Merge branch 'bpf-enforce-btf-pointer-write-checks-for-global-args'

Nuoqi Gui says:

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bpf: Enforce BTF pointer write checks for global args

check_mem_reg() verifies both read and write access when a caller passes
memory into a global subprogram. For PTR_TO_BTF_ID callers,
check_helper_mem_access() currently always checks the access as BPF_READ.

That lets a tracing program pass a task_struct field pointer to a global
subprogram argument typed as writable memory. The direct field store is rejected
with "only read is supported", but the callee is validated with a generic
writable PTR_TO_MEM argument and can store through it.

Forward the requested access type into the PTR_TO_BTF_ID helper-access path and
add verifier coverage for the global-subprogram argument case.

Validation (tested on bpf-next 8496d9020ff3):

  Without this series:
    direct BTF field store rejected with "only read is supported";
    global-subprogram candidate loaded, attached, and runtime-confirmed.

  With this series applied:
    direct BTF field store rejected with "only read is supported";
    global-subprogram candidate rejected with "only read is supported".

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
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====================

Link: https://patch.msgid.link/20260609-f01-04-btf-writable-arg-v1-0-f449cd970669@mails.tsinghua.edu.cn
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>