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Andrii Nakryiko says: ==================== Harden and extend ELF build ID parsing logic The goal of this patch set is to extend existing ELF build ID parsing logic, currently mostly used by BPF subsystem, with support for working in sleepable mode in which memory faults are allowed and can be relied upon to fetch relevant parts of ELF file to find and fetch .note.gnu.build-id information. This is useful and important for BPF subsystem itself, but also for PROCMAP_QUERY ioctl(), built atop of /proc/<pid>/maps functionality (see [0]), which makes use of the same build_id_parse() functionality. PROCMAP_QUERY is always called from sleepable user process context, so it doesn't have to suffer from current restrictions of build_id_parse() which are due to the NMI context assumption. Along the way, we harden the logic to avoid TOCTOU, overflow, out-of-bounds access problems. This is the very first patch, which can be backported to older releases, if necessary. We also lift existing limitations of only working as long as ELF program headers and build ID note section is contained strictly within the very first page of ELF file. We achieve all of the above without duplication of logic between sleepable and non-sleepable modes through freader abstraction that manages underlying folio from page cache (on demand) and gives a simple to use direct memory access interface. With that, single page restrictions and adding sleepable mode support is rather straightforward. We also extend existing set of BPF selftests with a few tests targeting build ID logic across sleepable and non-sleepabe contexts (we utilize sleepable and non-sleepable uprobes for that). [0] https://lore.kernel.org/linux-mm/20240627170900.1672542-4-andrii@kernel.org/ v6->v7: - added filemap_invalidate_{lock,unlock}_shared() around read_cache_folio and kept Eduard's Reviewed-by (Eduard); v5->v6: - use local phnum variable in get_build_id_32() (Jann); - switch memcmp() instead of strcmp() in parse_build_id() (Jann); v4->v5: - pass proper file reference to read_cache_folio() (Shakeel); - fix another potential overflow due to two u32 additions (Andi); - add PageUptodate() check to patch #1 (Jann); v3->v4: - fix few more potential overflow and out-of-bounds access issues (Andi); - use purely folio-based implementation for freader (Matthew); v2->v3: - remove unneeded READ_ONCE()s and force phoff to u64 for 32-bit mode (Andi); - moved hardening fixes to the front for easier backporting (Jann); - call freader_cleanup() from build_id_parse_buf() for consistency (Jiri); v1->v2: - ensure MADV_PAGEOUT works reliably by paging data in first (Shakeel); - to fix BPF CI build optionally define MADV_POPULATE_READ in selftest. ==================== Link: https://lore.kernel.org/r/20240829174232.3133883-1-andrii@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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| .get_maintainer.ignore | ||
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| README | ||
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 reStructuredText 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.