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AJvYcCWs8npqMsMgEMlbkjynryVa2t/g1KkpzB2goNMKpAOaG141R6eYNzQpTA7c3jeXU+wMR0in2Q0B/SmHkPI=@vger.kernel.org X-Gm-Message-State: AOJu0Yw5PPEqNUecTEZpSLvwsHcK4OCzcxCLSD0Sb0LYfw/mDHAMtdhf IdaPBXvKQLlJUcvMjt6Dx+w3XV/lHOIL+czA/0JLSBpqMKZh9xhOTqUaPJurU+VJNJfiZfauUGc 4hcid4Q== X-Google-Smtp-Source: AGHT+IG616iIEoJXepMEnFIXh2EvSXgtvB4OvHJFrlY3ghUherNjNwvIMu6DpxK7ywhW+VD5HsliaqgLk/2C X-Received: from anyblade.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:1791]) (user=mmaurer job=sendgmr) by 2002:a5b:d43:0:b0:e02:c06f:1db8 with SMTP id 3f1490d57ef6-e24d7b07255mr3692276.4.1727307575061; Wed, 25 Sep 2024 16:39:35 -0700 (PDT) Date: Wed, 25 Sep 2024 23:38:21 +0000 In-Reply-To: <20240925233854.90072-1-mmaurer@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240925233854.90072-1-mmaurer@google.com> X-Mailer: git-send-email 2.46.1.824.gd892dcdcdd-goog Message-ID: <20240925233854.90072-7-mmaurer@google.com> Subject: [PATCH v5 06/16] module: Factor out elf_validity_cache_index_mod From: Matthew Maurer To: masahiroy@kernel.org, ndesaulniers@google.com, ojeda@kernel.org, gary@garyguo.net, mcgrof@kernel.org, Alex Gaynor Cc: 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, linux-modules@vger.kernel.org, Matthew Maurer , Petr Pavlu , Sami Tolvanen , Daniel Gomez , Boqun Feng , " =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= " , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross Centralize .gnu.linkonce.this_module detection and property validation. Signed-off-by: Matthew Maurer --- kernel/module/main.c | 129 ++++++++++++++++++++++--------------------- 1 file changed, 67 insertions(+), 62 deletions(-) diff --git a/kernel/module/main.c b/kernel/module/main.c index 511d645ac577..ec638187ffcf 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -1919,6 +1919,68 @@ static int elf_validity_cache_index_info(struct load_info *info) return 0; } +/** + * elf_validity_cache_index_mod() - Validates and caches this_module section + * @info: Load info to cache this_module on. + * Must have &load_info->sechdrs and &load_info->secstrings populated + * + * The ".gnu.linkonce.this_module" ELF section is special. It is what modpost + * uses to refer to __this_module and let's use rely on THIS_MODULE to point + * to &__this_module properly. The kernel's modpost declares it on each + * modules's *.mod.c file. If the struct module of the kernel changes a full + * kernel rebuild is required. + * + * We have a few expectations for this special section, this function + * validates all this for us: + * + * * The section has contents + * * The section is unique + * * We expect the kernel to always have to allocate it: SHF_ALLOC + * * The section size must match the kernel's run time's struct module + * size + * + * If all checks pass, the index will be cached in &load_info->index.mod + * + * Return: %0 on validation success, %-ENOEXEC on failure + */ +static int elf_validity_cache_index_mod(struct load_info *info) +{ + Elf_Shdr *shdr; + int mod_idx; + + mod_idx = find_any_unique_sec(info, ".gnu.linkonce.this_module"); + if (mod_idx <= 0) { + pr_err("module %s: Exactly one .gnu.linkonce.this_module section must exist.\n", + info->name ?: "(missing .modinfo section or name field)"); + return -ENOEXEC; + } + + shdr = &info->sechdrs[mod_idx]; + + if (shdr->sh_type == SHT_NOBITS) { + pr_err("module %s: .gnu.linkonce.this_module section must have a size set\n", + info->name ?: "(missing .modinfo section or name field)"); + return -ENOEXEC; + } + + if (!(shdr->sh_flags & SHF_ALLOC)) { + pr_err("module %s: .gnu.linkonce.this_module must occupy memory during process execution\n", + info->name ?: "(missing .modinfo section or name field)"); + return -ENOEXEC; + } + + if (shdr->sh_size != sizeof(struct module)) { + pr_err("module %s: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time\n", + info->name ?: "(missing .modinfo section or name field)"); + return -ENOEXEC; + } + + info->index.mod = mod_idx; + + return 0; +} + + /* * Check userspace passed ELF module against our expectations, and cache * useful variables for further processing as we go. @@ -1944,7 +2006,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) unsigned int i; Elf_Shdr *shdr; int err; - unsigned int num_mod_secs = 0, mod_idx; unsigned int num_sym_secs = 0, sym_idx; err = elf_validity_cache_sechdrs(info); @@ -1954,16 +2015,15 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) if (err < 0) return err; err = elf_validity_cache_index_info(info); + if (err < 0) + return err; + err = elf_validity_cache_index_mod(info); if (err < 0) return err; for (i = 1; i < info->hdr->e_shnum; i++) { shdr = &info->sechdrs[i]; - switch (shdr->sh_type) { - case SHT_NULL: - case SHT_NOBITS: - continue; - case SHT_SYMTAB: + if (shdr->sh_type == SHT_SYMTAB) { if (shdr->sh_link == SHN_UNDEF || shdr->sh_link >= info->hdr->e_shnum) { pr_err("Invalid ELF sh_link!=SHN_UNDEF(%d) or (sh_link(%d) >= hdr->e_shnum(%d)\n", @@ -1973,14 +2033,6 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) } num_sym_secs++; sym_idx = i; - fallthrough; - default: - if (strcmp(info->secstrings + shdr->sh_name, - ".gnu.linkonce.this_module") == 0) { - num_mod_secs++; - mod_idx = i; - } - break; } } @@ -1996,55 +2048,8 @@ static int elf_validity_cache_copy(struct load_info *info, int flags) info->index.str = shdr->sh_link; info->strtab = (char *)info->hdr + info->sechdrs[info->index.str].sh_offset; - /* - * The ".gnu.linkonce.this_module" ELF section is special. It is - * what modpost uses to refer to __this_module and let's use rely - * on THIS_MODULE to point to &__this_module properly. The kernel's - * modpost declares it on each modules's *.mod.c file. If the struct - * module of the kernel changes a full kernel rebuild is required. - * - * We have a few expectaions for this special section, the following - * code validates all this for us: - * - * o Only one section must exist - * o We expect the kernel to always have to allocate it: SHF_ALLOC - * o The section size must match the kernel's run time's struct module - * size - */ - if (num_mod_secs != 1) { - pr_err("module %s: Only one .gnu.linkonce.this_module section must exist.\n", - info->name ?: "(missing .modinfo section or name field)"); - goto no_exec; - } - - shdr = &info->sechdrs[mod_idx]; - - /* - * This is already implied on the switch above, however let's be - * pedantic about it. - */ - if (shdr->sh_type == SHT_NOBITS) { - pr_err("module %s: .gnu.linkonce.this_module section must have a size set\n", - info->name ?: "(missing .modinfo section or name field)"); - goto no_exec; - } - - if (!(shdr->sh_flags & SHF_ALLOC)) { - pr_err("module %s: .gnu.linkonce.this_module must occupy memory during process execution\n", - info->name ?: "(missing .modinfo section or name field)"); - goto no_exec; - } - - if (shdr->sh_size != sizeof(struct module)) { - pr_err("module %s: .gnu.linkonce.this_module section size must match the kernel's built struct module size at run time\n", - info->name ?: "(missing .modinfo section or name field)"); - goto no_exec; - } - - info->index.mod = mod_idx; - /* This is temporary: point mod into copy of data. */ - info->mod = (void *)info->hdr + shdr->sh_offset; + info->mod = (void *)info->hdr + info->sechdrs[info->index.mod].sh_offset; /* * If we didn't load the .modinfo 'name' field earlier, fall back to