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2011fccfb6
Currently there is a difference in how verifier checks memory access for helper arguments for PTR_TO_MAP_VALUE and PTR_TO_STACK with regard to variable part of offset. check_map_access, that is used for PTR_TO_MAP_VALUE, can handle variable offsets just fine, so that BPF program can call a helper like this: some_helper(map_value_ptr + off, size); , where offset is unknown at load time, but is checked by program to be in a safe rage (off >= 0 && off + size < map_value_size). But it's not the case for check_stack_boundary, that is used for PTR_TO_STACK, and same code with pointer to stack is rejected by verifier: some_helper(stack_value_ptr + off, size); For example: 0: (7a) *(u64 *)(r10 -16) = 0 1: (7a) *(u64 *)(r10 -8) = 0 2: (61) r2 = *(u32 *)(r1 +0) 3: (57) r2 &= 4 4: (17) r2 -= 16 5: (0f) r2 += r10 6: (18) r1 = 0xffff888111343a80 8: (85) call bpf_map_lookup_elem#1 invalid variable stack read R2 var_off=(0xfffffffffffffff0; 0x4) Add support for variable offset access to check_stack_boundary so that if offset is checked by program to be in a safe range it's accepted by verifier. Signed-off-by: Andrey Ignatov <rdna@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.