Re: [PATCH v4 1/6] s390/kexec_file: Don't opencode appended signature check.

[Luis Chamberlain]

On Mon, Jan 10, 2022 at 02:49:53PM +0100, Michal Suchanek wrote:
> Module verification already implements appeded signature check.
> 
> Reuse it for kexec_file.
> 
> The kexec_file implementation uses EKEYREJECTED error in some cases when
> there is no key and the common implementation uses ENOPKG or EBADMSG
> instead.
> 
> Signed-off-by: Michal Suchanek 
> Acked-by: Heiko Carstens 
> ---
> v3: Philipp Rudo : Update the commit with note about
> change of return value
> ---
>  arch/s390/kernel/machine_kexec_file.c | 22 +-
>  1 file changed, 5 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/s390/kernel/machine_kexec_file.c 
> b/arch/s390/kernel/machine_kexec_file.c
> index 8f43575a4dd3..c944d71316c7 100644
> --- a/arch/s390/kernel/machine_kexec_file.c
> +++ b/arch/s390/kernel/machine_kexec_file.c
> @@ -31,6 +31,7 @@ int s390_verify_sig(const char *kernel, unsigned long 
> kernel_len)
>   const unsigned long marker_len = sizeof(MODULE_SIG_STRING) - 1;
>   struct module_signature *ms;
>   unsigned long sig_len;
> + int ret;
>  
>   /* Skip signature verification when not secure IPLed. */
>   if (!ipl_secure_flag)
> @@ -45,25 +46,12 @@ int s390_verify_sig(const char *kernel, unsigned long 
> kernel_len)
>   kernel_len -= marker_len;
>  
>   ms = (void *)kernel + kernel_len - sizeof(*ms);
> - kernel_len -= sizeof(*ms);
> + ret = mod_check_sig(ms, kernel_len, "kexec");
> + if (ret)
> + return ret;
>  
>   sig_len = be32_to_cpu(ms->sig_len);
> - if (sig_len >= kernel_len)
> - return -EKEYREJECTED;

There is a small minor fix here, where by using mod_check_sig() now
decreased the kernel_len by the sizeof(*ms). It is minor though.

> - kernel_len -= sig_len;
> -
> - if (ms->id_type != PKEY_ID_PKCS7)
> - return -EKEYREJECTED;

More importantly is the return value used here changes but given the
Ack by Heiko I suspect this if fine and does not break old userspace,
the only change here is the possible error value returned by the
kexec_file_load() system call.

Reviewed-by: Luis Chamberlain 

   Luis

[PATCH v4 1/6] s390/kexec_file: Don't opencode appended signature check.

[Michal Suchanek]

Module verification already implements appeded signature check.

Reuse it for kexec_file.

The kexec_file implementation uses EKEYREJECTED error in some cases when
there is no key and the common implementation uses ENOPKG or EBADMSG
instead.

Signed-off-by: Michal Suchanek 
Acked-by: Heiko Carstens 
---
v3: Philipp Rudo : Update the commit with note about
change of return value
---
 arch/s390/kernel/machine_kexec_file.c | 22 +-
 1 file changed, 5 insertions(+), 17 deletions(-)

diff --git a/arch/s390/kernel/machine_kexec_file.c 
b/arch/s390/kernel/machine_kexec_file.c
index 8f43575a4dd3..c944d71316c7 100644
--- a/arch/s390/kernel/machine_kexec_file.c
+++ b/arch/s390/kernel/machine_kexec_file.c
@@ -31,6 +31,7 @@ int s390_verify_sig(const char *kernel, unsigned long 
kernel_len)
const unsigned long marker_len = sizeof(MODULE_SIG_STRING) - 1;
struct module_signature *ms;
unsigned long sig_len;
+   int ret;
 
/* Skip signature verification when not secure IPLed. */
if (!ipl_secure_flag)
@@ -45,25 +46,12 @@ int s390_verify_sig(const char *kernel, unsigned long 
kernel_len)
kernel_len -= marker_len;
 
ms = (void *)kernel + kernel_len - sizeof(*ms);
-   kernel_len -= sizeof(*ms);
+   ret = mod_check_sig(ms, kernel_len, "kexec");
+   if (ret)
+   return ret;
 
sig_len = be32_to_cpu(ms->sig_len);
-   if (sig_len >= kernel_len)
-   return -EKEYREJECTED;
-   kernel_len -= sig_len;
-
-   if (ms->id_type != PKEY_ID_PKCS7)
-   return -EKEYREJECTED;
-
-   if (ms->algo != 0 ||
-   ms->hash != 0 ||
-   ms->signer_len != 0 ||
-   ms->key_id_len != 0 ||
-   ms->__pad[0] != 0 ||
-   ms->__pad[1] != 0 ||
-   ms->__pad[2] != 0) {
-   return -EBADMSG;
-   }
+   kernel_len -= sizeof(*ms) + sig_len;
 
return verify_pkcs7_signature(kernel, kernel_len,
  kernel + kernel_len, sig_len,
-- 
2.31.1