kernel/kexec_file.c: remove mis-use of sh_offset field during purgatory load

The current code uses the sh_offset field in purgatory_info->sechdrs to
store a pointer to the current load address of the section.  Depending
whether the section will be loaded or not this is either a pointer into
purgatory_info->purgatory_buf or kexec_purgatory.  This is not only a
violation of the ELF standard but also makes the code very hard to
understand as you cannot tell if the memory you are using is read-only
or not.

Remove this misuse and store the offset of the section in
pugaroty_info->purgatory_buf in sh_offset.

Link: http://lkml.kernel.org/r/20180321112751.22196-10-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, 7 insertions, 30 deletions

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 7b63de8a89b6..269116fd932c 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -790,6 +790,10 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
         Elf_Shdr *sechdrs;
         int i;
 
+        /*
+         * The section headers in kexec_purgatory are read-only. In order to
+         * have them modifiable make a temporary copy.
+         */
         sechdrs = vzalloc(pi->ehdr->e_shnum * sizeof(Elf_Shdr));
         if (!sechdrs)
                 return -ENOMEM;
@@ -797,28 +801,6 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
                pi->ehdr->e_shnum * sizeof(Elf_Shdr));
         pi->sechdrs = sechdrs;
 
-        /*
-         * We seem to have multiple copies of sections. First copy is which
-         * is embedded in kernel in read only section. Some of these sections
-         * will be copied to a temporary buffer and relocated. And these
-         * sections will finally be copied to their final destination at
-         * segment load time.
-         *
-         * Use ->sh_offset to reflect section address in memory. It will
-         * point to original read only copy if section is not allocatable.
-         * Otherwise it will point to temporary copy which will be relocated.
-         *
-         * Use ->sh_addr to contain final address of the section where it
-         * will go during execution time.
-         */
-        for (i = 0; i < pi->ehdr->e_shnum; i++) {
-                if (sechdrs[i].sh_type == SHT_NOBITS)
-                        continue;
-
-                sechdrs[i].sh_offset = (unsigned long)pi->ehdr +
-                                                sechdrs[i].sh_offset;
-        }
-
         offset = 0;
         bss_addr = kbuf->mem + kbuf->bufsz;
         kbuf->image->start = pi->ehdr->e_entry;
@@ -847,17 +829,12 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
                         kbuf->image->start += kbuf->mem + offset;
                 }
 
-                src = (void *)sechdrs[i].sh_offset;
+                src = (void *)pi->ehdr + sechdrs[i].sh_offset;
                 dst = pi->purgatory_buf + offset;
                 memcpy(dst, src, sechdrs[i].sh_size);
 
                 sechdrs[i].sh_addr = kbuf->mem + offset;
-
-                /*
-                 * This section got copied to temporary buffer. Update
-                 * ->sh_offset accordingly.
-                 */
-                sechdrs[i].sh_offset = (unsigned long)dst;
+                sechdrs[i].sh_offset = offset;
                 offset += sechdrs[i].sh_size;
         }
 
@@ -1067,7 +1044,7 @@ int kexec_purgatory_get_set_symbol(struct kimage *image, const char *name,
                 return -EINVAL;
         }
 
-        sym_buf = (char *)sec->sh_offset + sym->st_value;
+        sym_buf = (char *)pi->purgatory_buf + sec->sh_offset + sym->st_value;
 
         if (get_value)
                 memcpy((void *)buf, sym_buf, size);