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Message-ID: <20241015231651.3851138-7-mmaurer@google.com>
Date: Tue, 15 Oct 2024 23:16:40 +0000
From: Matthew Maurer <mmaurer@...gle.com>
To: mcgrof@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
samitolvanen@...gle.com, Matthew Maurer <mmaurer@...gle.com>,
Petr Pavlu <petr.pavlu@...e.com>, Daniel Gomez <da.gomez@...sung.com>
Subject: [PATCH 06/12] module: Factor out elf_validity_cache_index_mod
Centralize .gnu.linkonce.this_module detection and property validation.
Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
---
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 6747cbc774b0..b633347d5d98 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1952,6 +1952,68 @@ 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.
@@ -1977,7 +2039,6 @@ 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);
@@ -1987,16 +2048,15 @@ 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",
@@ -2006,14 +2066,6 @@ 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;
}
}
@@ -2029,55 +2081,8 @@ 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
--
2.47.0.rc1.288.g06298d1525-goog
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