From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit `objtool` errors such as: vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a: can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd The reason is that in such builds, the Clang invocation that compiles the combined Rust plus helpers bitcode emits LLVM bitcode (again) -- the final code generation happens in the linker's LTO step, which the `-mllvm` trap options passed to Clang do not reach. This, in turn, means that unreachable traps are missing, and the impossible paths do not merely fallthrough to the next symbol, but past the end of their own section, since LTO builds place each function in its own section. Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always emits machine code directly, with the traps in place. Assisted-by: LLM Cc: Gary Guo Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- lib/buildid.c | 407 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 407 insertions(+) create mode 100644 lib/buildid.c (limited to 'lib/buildid.c') diff --git a/lib/buildid.c b/lib/buildid.c new file mode 100644 index 000000000..c4b737640 --- /dev/null +++ b/lib/buildid.c @@ -0,0 +1,407 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include +#include +#include +#include +#include + +#define BUILD_ID 3 + +#define MAX_PHDR_CNT 256 + +void freader_init_from_file(struct freader *r, void *buf, u32 buf_sz, + struct file *file, bool may_fault) +{ + memset(r, 0, sizeof(*r)); + r->buf = buf; + r->buf_sz = buf_sz; + r->file = file; + r->may_fault = may_fault; +} + +void freader_init_from_mem(struct freader *r, const char *data, u64 data_sz) +{ + memset(r, 0, sizeof(*r)); + r->data = data; + r->data_sz = data_sz; +} + +static void freader_put_folio(struct freader *r) +{ + if (!r->folio) + return; + kunmap_local(r->addr); + folio_put(r->folio); + r->folio = NULL; +} + +static int freader_get_folio(struct freader *r, loff_t file_off) +{ + /* check if we can just reuse current folio */ + if (r->folio && file_off >= r->folio_off && + file_off < r->folio_off + folio_size(r->folio)) + return 0; + + freader_put_folio(r); + + /* only use page cache lookup - fail if not already cached */ + r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT); + + if (IS_ERR(r->folio) || !folio_test_uptodate(r->folio)) { + if (!IS_ERR(r->folio)) + folio_put(r->folio); + r->folio = NULL; + return -EFAULT; + } + + r->folio_off = folio_pos(r->folio); + r->addr = kmap_local_folio(r->folio, 0); + + return 0; +} + +const void *freader_fetch(struct freader *r, loff_t file_off, size_t sz) +{ + size_t folio_sz; + + /* provided internal temporary buffer should be sized correctly */ + if (WARN_ON(r->buf && sz > r->buf_sz)) { + r->err = -E2BIG; + return NULL; + } + + if (unlikely(file_off + sz < file_off)) { + r->err = -EOVERFLOW; + return NULL; + } + + /* working with memory buffer is much more straightforward */ + if (!r->buf) { + if (file_off + sz > r->data_sz) { + r->err = -ERANGE; + return NULL; + } + return r->data + file_off; + } + + /* reject secretmem folios created with memfd_secret() */ + if (secretmem_mapping(r->file->f_mapping)) { + r->err = -EFAULT; + return NULL; + } + + /* use __kernel_read() for sleepable context */ + if (r->may_fault) { + ssize_t ret; + + ret = __kernel_read(r->file, r->buf, sz, &file_off); + if (ret != sz) { + r->err = (ret < 0) ? ret : -EIO; + return NULL; + } + return r->buf; + } + + /* fetch or reuse folio for given file offset */ + r->err = freader_get_folio(r, file_off); + if (r->err) + return NULL; + + /* if requested data is crossing folio boundaries, we have to copy + * everything into our local buffer to keep a simple linear memory + * access interface + */ + folio_sz = folio_size(r->folio); + if (file_off + sz > r->folio_off + folio_sz) { + u64 part_sz = r->folio_off + folio_sz - file_off, off; + + memcpy(r->buf, r->addr + file_off - r->folio_off, part_sz); + off = part_sz; + + while (off < sz) { + /* fetch next folio */ + r->err = freader_get_folio(r, r->folio_off + folio_sz); + if (r->err) + return NULL; + folio_sz = folio_size(r->folio); + part_sz = min_t(u64, sz - off, folio_sz); + memcpy(r->buf + off, r->addr, part_sz); + off += part_sz; + } + + return r->buf; + } + + /* if data fits in a single folio, just return direct pointer */ + return r->addr + (file_off - r->folio_off); +} + +void freader_cleanup(struct freader *r) +{ + if (!r->buf) + return; /* non-file-backed mode */ + + freader_put_folio(r); +} + +/* + * Parse build id from the note segment. This logic can be shared between + * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are + * identical. + */ +static int parse_build_id(struct freader *r, unsigned char *build_id, __u32 *size, + loff_t note_off, Elf32_Word note_size) +{ + const char note_name[] = "GNU"; + const size_t note_name_sz = sizeof(note_name); + u32 build_id_off, new_off, note_end, name_sz, desc_sz; + const Elf32_Nhdr *nhdr; + const char *data; + + if (check_add_overflow(note_off, note_size, ¬e_end)) + return -EINVAL; + + while (note_end - note_off > sizeof(Elf32_Nhdr) + note_name_sz) { + nhdr = freader_fetch(r, note_off, sizeof(Elf32_Nhdr) + note_name_sz); + if (!nhdr) + return r->err; + + name_sz = READ_ONCE(nhdr->n_namesz); + desc_sz = READ_ONCE(nhdr->n_descsz); + + new_off = note_off + sizeof(Elf32_Nhdr); + if (check_add_overflow(new_off, ALIGN(name_sz, 4), &new_off) || + check_add_overflow(new_off, ALIGN(desc_sz, 4), &new_off) || + new_off > note_end) + break; + + if (nhdr->n_type == BUILD_ID && + name_sz == note_name_sz && + memcmp(nhdr + 1, note_name, note_name_sz) == 0 && + desc_sz > 0 && desc_sz <= BUILD_ID_SIZE_MAX) { + build_id_off = note_off + sizeof(Elf32_Nhdr) + ALIGN(note_name_sz, 4); + + /* freader_fetch() will invalidate nhdr pointer */ + data = freader_fetch(r, build_id_off, desc_sz); + if (!data) + return r->err; + + memcpy(build_id, data, desc_sz); + memset(build_id + desc_sz, 0, BUILD_ID_SIZE_MAX - desc_sz); + if (size) + *size = desc_sz; + return 0; + } + + note_off = new_off; + } + + return -EINVAL; +} + +/* Parse build ID from 32-bit ELF */ +static int get_build_id_32(struct freader *r, unsigned char *build_id, __u32 *size) +{ + const Elf32_Ehdr *ehdr; + const Elf32_Phdr *phdr; + __u32 phnum, phoff, i; + + ehdr = freader_fetch(r, 0, sizeof(Elf32_Ehdr)); + if (!ehdr) + return r->err; + + /* subsequent freader_fetch() calls invalidate pointers, so remember locally */ + phnum = READ_ONCE(ehdr->e_phnum); + phoff = READ_ONCE(ehdr->e_phoff); + + /* set upper bound on amount of segments (phdrs) we iterate */ + if (phnum > MAX_PHDR_CNT) + phnum = MAX_PHDR_CNT; + + /* check that phoff is not large enough to cause an overflow */ + if (phoff + phnum * sizeof(Elf32_Phdr) < phoff) + return -EINVAL; + + for (i = 0; i < phnum; ++i) { + phdr = freader_fetch(r, phoff + i * sizeof(Elf32_Phdr), sizeof(Elf32_Phdr)); + if (!phdr) + return r->err; + + if (phdr->p_type == PT_NOTE && + !parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset), + READ_ONCE(phdr->p_filesz))) + return 0; + } + return -EINVAL; +} + +/* Parse build ID from 64-bit ELF */ +static int get_build_id_64(struct freader *r, unsigned char *build_id, __u32 *size) +{ + const Elf64_Ehdr *ehdr; + const Elf64_Phdr *phdr; + __u32 phnum, i; + __u64 phoff; + + ehdr = freader_fetch(r, 0, sizeof(Elf64_Ehdr)); + if (!ehdr) + return r->err; + + /* subsequent freader_fetch() calls invalidate pointers, so remember locally */ + phnum = READ_ONCE(ehdr->e_phnum); + phoff = READ_ONCE(ehdr->e_phoff); + + /* set upper bound on amount of segments (phdrs) we iterate */ + if (phnum > MAX_PHDR_CNT) + phnum = MAX_PHDR_CNT; + + /* check that phoff is not large enough to cause an overflow */ + if (phoff + phnum * sizeof(Elf64_Phdr) < phoff) + return -EINVAL; + + for (i = 0; i < phnum; ++i) { + phdr = freader_fetch(r, phoff + i * sizeof(Elf64_Phdr), sizeof(Elf64_Phdr)); + if (!phdr) + return r->err; + + if (phdr->p_type == PT_NOTE && + !parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset), + READ_ONCE(phdr->p_filesz))) + return 0; + } + + return -EINVAL; +} + +/* enough for Elf64_Ehdr, Elf64_Phdr, and all the smaller requests */ +#define MAX_FREADER_BUF_SZ 64 + +static int __build_id_parse(struct file *file, unsigned char *build_id, + __u32 *size, bool may_fault) +{ + const Elf32_Ehdr *ehdr; + struct freader r; + char buf[MAX_FREADER_BUF_SZ]; + int ret; + + freader_init_from_file(&r, buf, sizeof(buf), file, may_fault); + + /* fetch first 18 bytes of ELF header for checks */ + ehdr = freader_fetch(&r, 0, offsetofend(Elf32_Ehdr, e_type)); + if (!ehdr) { + ret = r.err; + goto out; + } + + ret = -EINVAL; + + /* compare magic x7f "ELF" */ + if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0) + goto out; + + /* only support executable file and shared object file */ + if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) + goto out; + + if (ehdr->e_ident[EI_CLASS] == ELFCLASS32) + ret = get_build_id_32(&r, build_id, size); + else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64) + ret = get_build_id_64(&r, build_id, size); +out: + freader_cleanup(&r); + return ret; +} + +/** + * build_id_parse_nofault() - Parse build ID of ELF file mapped to vma + * @vma: vma object + * @build_id: buffer to store build id, at least BUILD_ID_SIZE long + * @size: returns actual build id size in case of success + * + * Assumes no page fault can be taken, so if relevant portions of ELF file are + * not already paged in, fetching of build ID fails. + * + * Return: 0 on success; negative error, otherwise + */ +int build_id_parse_nofault(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size) +{ + if (!vma->vm_file) + return -EINVAL; + + return __build_id_parse(vma->vm_file, build_id, size, false /* !may_fault */); +} + +/** + * build_id_parse() - Parse build ID of ELF file mapped to VMA + * @vma: vma object + * @build_id: buffer to store build id, at least BUILD_ID_SIZE long + * @size: returns actual build id size in case of success + * + * Assumes faultable context and can cause page faults to bring in file data + * into page cache. + * + * Return: 0 on success; negative error, otherwise + */ +int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size) +{ + if (!vma->vm_file) + return -EINVAL; + + return __build_id_parse(vma->vm_file, build_id, size, true /* may_fault */); +} + +/** + * build_id_parse_file() - Parse build ID of ELF file + * @file: file object + * @build_id: buffer to store build id, at least BUILD_ID_SIZE long + * @size: returns actual build id size in case of success + * + * Assumes faultable context and can cause page faults to bring in file data + * into page cache. + * + * Return: 0 on success; negative error, otherwise + */ +int build_id_parse_file(struct file *file, unsigned char *build_id, __u32 *size) +{ + return __build_id_parse(file, build_id, size, true /* may_fault */); +} + +/** + * build_id_parse_buf - Get build ID from a buffer + * @buf: ELF note section(s) to parse + * @buf_size: Size of @buf in bytes + * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long + * + * Return: 0 on success, -EINVAL otherwise + */ +int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size) +{ + struct freader r; + int err; + + freader_init_from_mem(&r, buf, buf_size); + + err = parse_build_id(&r, build_id, NULL, 0, buf_size); + + freader_cleanup(&r); + return err; +} + +#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_VMCORE_INFO) +unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init; + +/** + * init_vmlinux_build_id - Compute and stash the running kernel's build ID + */ +void __init init_vmlinux_build_id(void) +{ + extern const void __start_notes; + extern const void __stop_notes; + unsigned int size = &__stop_notes - &__start_notes; + + build_id_parse_buf(&__start_notes, vmlinux_build_id, size); +} +#endif -- cgit v1.3.1