[PATCH 04/17] kexec_file: Search symbols in read-only kexec_purgatory

From: Philipp Rudo
Date: Fri Feb 02 2018 - 08:07:58 EST


The stripped purgatory does not contain a symtab. So when looking for
symbols this is done in read-only kexec_purgatory. Highlight this by
marking the corresponding variables as 'const'.

Signed-off-by: Philipp Rudo <prudo@xxxxxxxxxxxxxxxxxx>
---
kernel/kexec_file.c | 38 ++++++++++++++++++++++----------------
1 file changed, 22 insertions(+), 16 deletions(-)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 06fc9fdd2474..2072b288ec53 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -901,20 +901,27 @@ int kexec_load_purgatory(struct kimage *image, unsigned long min,
return ret;
}

-static Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
- const char *name)
+/*
+ * kexec_purgatory_find_symbol - find a symbol in the purgatory
+ * @pi: Purgatory to search in.
+ * @name: Name of the symbol.
+ *
+ * Return: pointer to symbol in read-only symtab on success, NULL on error.
+ */
+static const Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
+ const char *name)
{
+ const Elf_Shdr *sechdrs;
const Elf_Ehdr *ehdr;
- Elf_Sym *syms;
- Elf_Shdr *sechdrs;
- int i, k;
+ const Elf_Sym *syms;
const char *strtab;
+ int i, k;

- if (!pi->sechdrs || !pi->ehdr)
+ if (!pi->ehdr)
return NULL;

- sechdrs = pi->sechdrs;
ehdr = pi->ehdr;
+ sechdrs = (void *)ehdr + ehdr->e_shoff;

for (i = 0; i < ehdr->e_shnum; i++) {
if (sechdrs[i].sh_type != SHT_SYMTAB)
@@ -923,8 +930,8 @@ static Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
if (sechdrs[i].sh_link >= ehdr->e_shnum)
/* Invalid strtab section number */
continue;
- strtab = (char *)sechdrs[sechdrs[i].sh_link].sh_offset;
- syms = (Elf_Sym *)sechdrs[i].sh_offset;
+ strtab = (void *)ehdr + sechdrs[sechdrs[i].sh_link].sh_offset;
+ syms = (void *)ehdr + sechdrs[i].sh_offset;

/* Go through symbols for a match */
for (k = 0; k < sechdrs[i].sh_size/sizeof(Elf_Sym); k++) {
@@ -952,7 +959,7 @@ static Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
void *kexec_purgatory_get_symbol_addr(struct kimage *image, const char *name)
{
struct purgatory_info *pi = &image->purgatory_info;
- Elf_Sym *sym;
+ const Elf_Sym *sym;
Elf_Shdr *sechdr;

sym = kexec_purgatory_find_symbol(pi, name);
@@ -975,9 +982,9 @@ void *kexec_purgatory_get_symbol_addr(struct kimage *image, const char *name)
int kexec_purgatory_get_set_symbol(struct kimage *image, const char *name,
void *buf, unsigned int size, bool get_value)
{
- Elf_Sym *sym;
- Elf_Shdr *sechdrs;
struct purgatory_info *pi = &image->purgatory_info;
+ const Elf_Sym *sym;
+ Elf_Shdr *sec;
char *sym_buf;

sym = kexec_purgatory_find_symbol(pi, name);
@@ -990,16 +997,15 @@ int kexec_purgatory_get_set_symbol(struct kimage *image, const char *name,
return -EINVAL;
}

- sechdrs = pi->sechdrs;
+ sec = pi->sechdrs + sym->st_shndx;

- if (sechdrs[sym->st_shndx].sh_type == SHT_NOBITS) {
+ if (sec->sh_type == SHT_NOBITS) {
pr_err("symbol %s is in a bss section. Cannot %s\n", name,
get_value ? "get" : "set");
return -EINVAL;
}

- sym_buf = (unsigned char *)sechdrs[sym->st_shndx].sh_offset +
- sym->st_value;
+ sym_buf = (char *)sec->sh_offset + sym->st_value;

if (get_value)
memcpy((void *)buf, sym_buf, size);
--
2.13.5