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Re: [Xen-devel] [PATCH v4 07/16] livepatch/arm/x86: Check payload for for unwelcomed symbols.

On 19/09/2016 16:11, Jan Beulich wrote:
On 19.09.16 at 15:33, <julien.grall@xxxxxxx> wrote:
On 19/09/2016 11:27, Jan Beulich wrote:
On 16.09.16 at 18:38, <konrad.wilk@xxxxxxxxxx> wrote:
--- a/xen/arch/arm/livepatch.c
+++ b/xen/arch/arm/livepatch.c
@@ -117,6 +117,20 @@ bool arch_livepatch_symbol_ok(const struct livepatch_elf
     return true;

+bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
+                                const struct livepatch_elf_sym *sym)
+#ifdef CONFIG_ARM_32
+    /*
+     * Xen does not use Thumb instructions - and we should not see any of
+     * them. If we do, abort.
+     */
+    if ( sym->name && *sym->name == '$' && sym->name[1] == 't' )

Please use sym->name[0] for readability. Also, you may want to check the
length of the symbol before checking the second character.

Why would the length check be needed? If the first character is $,
then looking at the second one is always valid (and it being nul will
be properly dealt with by the expression above).

Because you may have a payload which is not valid? Or maybe you consider that all the payload are trusted.


Julien Grall

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