kernel/kexec_file.c: search symbols in read-only kexec_purgatory

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'.

Link: http://lkml.kernel.org/r/20180321112751.22196-5-prudo@linux.vnet.ibm.com
Signed-off-by: Philipp Rudo <prudo@linux.vnet.ibm.com>
Acked-by: Dave Young <dyoung@redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 22 insertions, 16 deletions

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 12cf9c9ff0bc..9bd1ec1dd875 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -962,20 +962,27 @@ out:
         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)
@@ -984,8 +991,8 @@ 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++) {
@@ -1013,7 +1020,7 @@ 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);
@@ -1036,9 +1043,9 @@ 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);
@@ -1051,16 +1058,15 @@ 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);