[Xen-devel] [PATCH v4 02/11] livepatch: Tighten alignment checks.

[Konrad Rzeszutek Wilk <konrad@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.

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
Cc: Ross Lagerwall <ross.lagerwall@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.
v3: Change the two checks to be per Jan's recommendations.
v4: Add Jan's Reviewed-by.
    Swap the two conditionals around.
---
 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..dd8b47a1fa 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 & (sec[i].sec->sh_addralign - 1) )
+        {
+            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_addralign &&
+                  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_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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