linux-kernel - [PATCH v3 02/16] module: Factor out elf_validity

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Message-ID: <20240806212106.617164-3-mmaurer@google.com>
Date: Tue,  6 Aug 2024 21:20:28 +0000
From: Matthew Maurer <mmaurer@...gle.com>
To: masahiroy@...nel.org, ndesaulniers@...gle.com, ojeda@...nel.org, 
	gary@...yguo.net, mcgrof@...nel.org, Alex Gaynor <alex.gaynor@...il.com>, 
	Wedson Almeida Filho <wedsonaf@...il.com>
Cc: Matthew Maurer <mmaurer@...gle.com>, rust-for-linux@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, neal@...pa.dev, 
	marcan@...can.st, j@...nau.net, asahi@...ts.linux.dev, 
	Boqun Feng <boqun.feng@...il.com>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...sung.com>, Alice Ryhl <aliceryhl@...gle.com>, 
	linux-modules@...r.kernel.org
Subject: [PATCH v3 02/16] module: Factor out elf_validity_ehdr

Factor out verification of the ELF header and document what is checked.

Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
---
 kernel/module/main.c | 70 +++++++++++++++++++++++++++++---------------
 1 file changed, 47 insertions(+), 23 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 141a964b6b13..1218cc7e1196 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1664,6 +1664,50 @@ static int validate_section_offset(const struct load_info *info, Elf_Shdr *shdr)
 	return 0;
 }
 
+/**
+ * elf_validity_ehdr() - Checks an ELF header for module validity
+ * @info: Load info containing the ELF header to check
+ *
+ * Checks whether an ELF header could belong to a valid module. Checks:
+ *
+ * * ELF header is within the data the user provided
+ * * ELF magic is present
+ * * It is relocatable (not final linked, not core file, etc.)
+ * * The header's machine type matches what the architecture expects.
+ * * Optional arch-specific hook for other properties
+ *   - module_elf_check_arch() is currently only used by PPC to check
+ *   ELF ABI version, but may be used by others in the future.
+ *
+ * Return: %0 if valid, %-ENOEXEC on failure.
+ */
+static int elf_validity_ehdr(const struct load_info *info)
+{
+	if (info->len < sizeof(*(info->hdr))) {
+		pr_err("Invalid ELF header len %lu\n", info->len);
+		return -ENOEXEC;
+	}
+	if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0) {
+		pr_err("Invalid ELF header magic: != %s\n", ELFMAG);
+		return -ENOEXEC;
+	}
+	if (info->hdr->e_type != ET_REL) {
+		pr_err("Invalid ELF header type: %u != %u\n",
+		       info->hdr->e_type, ET_REL);
+		return -ENOEXEC;
+	}
+	if (!elf_check_arch(info->hdr)) {
+		pr_err("Invalid architecture in ELF header: %u\n",
+		       info->hdr->e_machine);
+		return -ENOEXEC;
+	}
+	if (!module_elf_check_arch(info->hdr)) {
+		pr_err("Invalid module architecture in ELF header: %u\n",
+		       info->hdr->e_machine);
+		return -ENOEXEC;
+	}
+	return 0;
+}
+
 /*
  * Check userspace passed ELF module against our expectations, and cache
  * useful variables for further processing as we go.
@@ -1693,30 +1737,10 @@ 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;
 
-	if (info->len < sizeof(*(info->hdr))) {
-		pr_err("Invalid ELF header len %lu\n", info->len);
-		goto no_exec;
-	}
+	err = elf_validity_ehdr(info);
+	if (err < 0)
+		return err;
 
-	if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0) {
-		pr_err("Invalid ELF header magic: != %s\n", ELFMAG);
-		goto no_exec;
-	}
-	if (info->hdr->e_type != ET_REL) {
-		pr_err("Invalid ELF header type: %u != %u\n",
-		       info->hdr->e_type, ET_REL);
-		goto no_exec;
-	}
-	if (!elf_check_arch(info->hdr)) {
-		pr_err("Invalid architecture in ELF header: %u\n",
-		       info->hdr->e_machine);
-		goto no_exec;
-	}
-	if (!module_elf_check_arch(info->hdr)) {
-		pr_err("Invalid module architecture in ELF header: %u\n",
-		       info->hdr->e_machine);
-		goto no_exec;
-	}
 	if (info->hdr->e_shentsize != sizeof(Elf_Shdr)) {
 		pr_err("Invalid ELF section header size\n");
 		goto no_exec;
-- 
2.46.0.rc2.264.g509ed76dc8-goog