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Eduard Zingerman says:
====================
This patch-set is a part of preparation work for -mcpu=v4 option for
BPF C compiler (discussed in [1]). Among other things -mcpu=v4 should
enable generation of BPF_ST instruction by the compiler.
- Patches #1,2 adjust verifier to track values of constants written to
stack using BPF_ST. Currently these are tracked imprecisely, unlike
the writes using BPF_STX, e.g.:
fp[-8] = 42; currently verifier assumes that fp[-8]=mmmmmmmm
after such instruction, where m stands for "misc",
just a note that something is written at fp[-8].
r1 = 42; verifier tracks r1=42 after this instruction.
fp[-8] = r1; verifier tracks fp[-8]=42 after this instruction.
This patch makes both cases equivalent.
- Patches #3,4 adjust verifier.c:check_stack_write_fixed_off() to
preserve STACK_ZERO marks when BPF_ST writes zero. Currently these
are replaced by STACK_MISC, unlike zero writes using BPF_STX, e.g.:
... stack range [X,Y] is marked as STACK_ZERO ...
r0 = ... variable offset pointer to stack with range [X,Y] ...
fp[r0] = 0; currently verifier marks range [X,Y] as
STACK_MISC for such instructions.
r1 = 0;
fp[r0] = r1; verifier keeps STACK_ZERO marks for range [X,Y].
This patch makes both cases equivalent.
Motivating example for patch #1 could be found at [3].
Previous version of the patch-set is here [2], the changes are:
- Explicit initialization of fake register parent link is removed from
verifier.c:check_stack_write_fixed_off() as parent links are now
correctly handled by verifier.c:save_register_state().
- Original patch #1 is split in patches #1 & #3.
- Missing test case added for patch #3
verifier.c:check_stack_write_fixed_off() adjustment.
- Test cases are updated to use .prog_type = BPF_PROG_TYPE_SK_LOOKUP,
which requires return value to be in the range [0,1] (original test
cases assumed that such range is always required, which is not true).
- Original patch #3 with changes allowing BPF_ST writes to context is
withheld for now, w/o compiler support for BPF_ST it requires some
creative testing.
- Original patch #5 is removed from the patch-set. This patch
contained adjustments to expected verifier error messages in some
tests, necessary when C compiler generates BPF_ST instruction
instead of BPF_STX (changes to expected instruction indices). These
changes are not necessary yet.
[1] https://lore.kernel.org/bpf/01515302-c37d-2ee5-c950-2f556a4caad0@meta.com/
[2] https://lore.kernel.org/bpf/20221231163122.1360813-1-eddyz87@gmail.com/
[3] https://lore.kernel.org/bpf/f1e4282bf00aa21a72fc5906f8c3be1ae6c94a5e.camel@gmail.com/
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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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.