[Xen-devel] [PATCH v2 1/5] livepatch: Tighten alignment checks.

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

The ELF specification mentions nothing about the sh_size being
modulo the sh_addralign. Only that sh_addr MUST be aligned on
sh_addralign if sh_addralign is not zero or one.

We on loading did not take this in-to account so this patch adds
a check on the ELF file as it is being parsed.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
v1: Initial patch
v2: Drop the check when loading it in memory
    Add check for alignment being anything but power of two (ignoring 0, and 1)
    Change dprintk to include hex values and print addr not size.
---
 xen/common/livepatch_elf.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/xen/common/livepatch_elf.c b/xen/common/livepatch_elf.c
index b69e2718dd..4dc1b68871 100644
--- a/xen/common/livepatch_elf.c
+++ b/xen/common/livepatch_elf.c
@@ -86,6 +86,19 @@ static int elf_resolve_sections(struct livepatch_elf *elf, 
const void *data)
                     delta < sizeof(Elf_Ehdr) ? "at ELF header" : "is past 
end");
             return -EINVAL;
         }
+        else if ( sec[i].sec->sh_addralign > 1 &&
+                  sec[i].sec->sh_addr % sec[i].sec->sh_addralign )
+        {
+            dprintk(XENLOG_ERR, LIVEPATCH "%s: Section [%u] addr 
(%#"PRIxElfAddr") is not aligned properly (%#"PRIxElfAddr")\n",
+                    elf->name, i, sec[i].sec->sh_addr, 
sec[i].sec->sh_addralign);
+            return -EINVAL;
+        }
+        else if ( sec[i].sec->sh_addralign > 1 && sec[i].sec->sh_addralign % 2 
)
+        {
+            dprintk(XENLOG_ERR, LIVEPATCH "%s: Section [%u] alignment 
(%#"PRIxElfAddr") is not supported\n",
+                    elf->name, i, sec[i].sec->sh_addralign);
+            return -EOPNOTSUPP;
+        }
         else if ( (sec[i].sec->sh_flags & (SHF_WRITE | SHF_ALLOC)) &&
                   sec[i].sec->sh_type == SHT_NOBITS &&
                   sec[i].sec->sh_size > LIVEPATCH_MAX_SIZE )
-- 
2.13.3


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