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AJvYcCXP4oxoMYpHeWMcgj8YUk3L2+o11So7/g/8XHjWFDp674FiR/evnAx+4GLSOm5WW6GSj5ozSqhJ7EUBckz9ZK74cISDKeDoqTmgur4U X-Gm-Message-State: AOJu0Yx3QmOTMZbpiREAI+TovuS/MbXaQ3I6HgcLRil3w+/smikc/6i8 aYVzwFrj9oatmVh985/9oE075+o7Mk1M9Re1Z9ppTtOBPD92uueQ+X4v5nzHp6mC799+RywmDzT Kw8Jrkw== X-Google-Smtp-Source: AGHT+IFSYvmkaodRJOM+NJzUc1TZcIArEkVrs4l6TsWHjv221yZbaqYbrPbNVyJZ/JmOpD2YsJPdd4415EZ+ X-Received: from anyblade.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:1791]) (user=mmaurer job=sendgmr) by 2002:a05:6902:118f:b0:e0e:4e5d:c414 with SMTP id 3f1490d57ef6-e0e4e5dc564mr88686276.10.1722979276827; Tue, 06 Aug 2024 14:21:16 -0700 (PDT) Date: Tue, 6 Aug 2024 21:20:29 +0000 In-Reply-To: <20240806212106.617164-1-mmaurer@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240806212106.617164-1-mmaurer@google.com> X-Mailer: git-send-email 2.46.0.rc2.264.g509ed76dc8-goog Message-ID: <20240806212106.617164-4-mmaurer@google.com> Subject: [PATCH v3 03/16] module: Factor out elf_validity_cache_sechdrs From: Matthew Maurer To: masahiroy@kernel.org, ndesaulniers@google.com, ojeda@kernel.org, gary@garyguo.net, mcgrof@kernel.org, Alex Gaynor , Wedson Almeida Filho Cc: Matthew Maurer , rust-for-linux@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, neal@gompa.dev, marcan@marcan.st, j@jannau.net, asahi@lists.linux.dev, Boqun Feng , " =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= " , Benno Lossin , Andreas Hindborg , Alice Ryhl , linux-modules@vger.kernel.org Factor out and document the validation of section headers. Because we now validate all section offsets and lengths before accessing them, we can remove the ad-hoc checks. Signed-off-by: Matthew Maurer --- kernel/module/main.c | 125 ++++++++++++++++++++++++++++--------------- 1 file changed, 82 insertions(+), 43 deletions(-) diff --git a/kernel/module/main.c b/kernel/module/main.c index 1218cc7e1196..c480fd33861a 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -1708,6 +1708,87 @@ static int elf_validity_ehdr(const struct load_info *info) return 0; } +/** + * elf_validity_cache_sechdrs() - Cache section headers if valid + * @info: Load info to compute section headers from + * + * Checks: + * + * * ELF header is valid (see elf_validity_ehdr()) + * * Section headers are the size we expect + * * Section array fits in the user provided data + * * Section index 0 is NULL + * * Section contents are inbounds + * + * Then updates @info with a &load_info->sechdrs pointer if valid. + * + * Return: %0 if valid, negative error code if validation failed. + */ +static int elf_validity_cache_sechdrs(struct load_info *info) +{ + Elf_Shdr *sechdrs; + Elf_Shdr *shdr; + int i; + int err; + + err = elf_validity_ehdr(info); + if (err < 0) + return err; + + if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) { + pr_err("Invalid ELF section header size\n"); + return -ENOEXEC; + } + + /* + * e_shnum is 16 bits, and sizeof(Elf_Shdr) is + * known and small. So e_shnum * sizeof(Elf_Shdr) + * will not overflow unsigned long on any platform. + */ + if (info->hdr->e_shoff >= info->len + || (info->hdr->e_shnum * sizeof(Elf_Shdr) > + info->len - info->hdr->e_shoff)) { + pr_err("Invalid ELF section header overflow\n"); + return -ENOEXEC; + } + + sechdrs = (void *)info->hdr + info->hdr->e_shoff; + + /* + * The code assumes that section 0 has a length of zero and + * an addr of zero, so check for it. + */ + if (sechdrs[0].sh_type != SHT_NULL + || sechdrs[0].sh_size != 0 + || sechdrs[0].sh_addr != 0) { + pr_err("ELF Spec violation: section 0 type(%d)!=SH_NULL or non-zero len or addr\n", + sechdrs[0].sh_type); + return -ENOEXEC; + } + + /* Validate contents are inbounds */ + for (i = 1; i < info->hdr->e_shnum; i++) { + shdr = &sechdrs[i]; + switch (shdr->sh_type) { + case SHT_NULL: + case SHT_NOBITS: + /* No contents, offset/size don't mean anything */ + continue; + default: + err = validate_section_offset(info, shdr); + if (err < 0) { + pr_err("Invalid ELF section in module (section %u type %u)\n", + i, shdr->sh_type); + return err; + } + } + } + + info->sechdrs = sechdrs; + + return 0; +} + /* * Check userspace passed ELF module against our expectations, and cache * useful variables for further processing as we go. @@ -1737,29 +1818,10 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) unsigned int num_info_secs = 0, info_idx; unsigned int num_sym_secs = 0, sym_idx; - err = elf_validity_ehdr(info); + err = elf_validity_cache_sechdrs(info); if (err < 0) return err; - if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) { - pr_err("Invalid ELF section header size\n"); - goto no_exec; - } - - /* - * e_shnum is 16 bits, and sizeof(Elf_Shdr) is - * known and small. So e_shnum * sizeof(Elf_Shdr) - * will not overflow unsigned long on any platform. - */ - if (info->hdr->e_shoff >= info->len - || (info->hdr->e_shnum * sizeof(Elf_Shdr) > - info->len - info->hdr->e_shoff)) { - pr_err("Invalid ELF section header overflow\n"); - goto no_exec; - } - - info->sechdrs = (void *)info->hdr + info->hdr->e_shoff; - /* * Verify if the section name table index is valid. */ @@ -1772,11 +1834,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) } strhdr = &info->sechdrs[info->hdr->e_shstrndx]; - err = validate_section_offset(info, strhdr); - if (err < 0) { - pr_err("Invalid ELF section hdr(type %u)\n", strhdr->sh_type); - return err; - } /* * The section name table must be NUL-terminated, as required @@ -1793,18 +1850,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) goto no_exec; } - /* - * The code assumes that section 0 has a length of zero and - * an addr of zero, so check for it. - */ - if (info->sechdrs[0].sh_type != SHT_NULL - || info->sechdrs[0].sh_size != 0 - || info->sechdrs[0].sh_addr != 0) { - pr_err("ELF Spec violation: section 0 type(%d)!=SH_NULL or non-zero len or addr\n", - info->sechdrs[0].sh_type); - goto no_exec; - } - for (i = 1; i < info->hdr->e_shnum; i++) { shdr = &info->sechdrs[i]; switch (shdr->sh_type) { @@ -1823,12 +1868,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) sym_idx = i; fallthrough; default: - err = validate_section_offset(info, shdr); - if (err < 0) { - pr_err("Invalid ELF section in module (section %u type %u)\n", - i, shdr->sh_type); - return err; - } if (strcmp(info->secstrings + shdr->sh_name, ".gnu.linkonce.this_module") == 0) { num_mod_secs++;