Re: [Linaro-uefi] [PATCH v3] xen/arm64: check XSM Magic and Signature from the second unknown module.

(Use Stefano's new e-mail address) Hi Fu Wei,

On 29/03/16 04:26, fu.wei@linaro.org wrote:

From: Fu Wei fu.wei@linaro.org

This patch add a check_xsm_signature static function for detecting XSM

s/add/adds/

from the second unknown module.

If Xen can't get the kind of module from compatible, we guess the kind of these first two unknown respectively:

The steps below are not only for the first two modules.

 (1) The first unknown must be kernel;
 (2) The second unknown is ramdisk, only if we have ramdisk;

This is unclear.

 (3) Start from the 2nd unknown, detect the XSM binary signature;
 (4) If we got XSM in the 2nd unknown, that means we don't load initrd.

s/initrd/ramdisk/

Also, the documentation in misc/arm/device-tree/booting.txt needs to be updated.

ARM behavior will be compatible to x86 and will simplify multi-arch bootloader such as GRUB, so I'm fine to introduce this boot protocol change. However, I'd like to see the reason of this change spells out in the commit message.

Signed-off-by: Fu Wei fu.wei@linaro.org

Changelog: v3: Using memcmp instead of strncmp. Using "return 0;" instead of panic(); Improve some comments.

v2: http://lists.xen.org/archives/html/xen-devel/2016-03/msg03543.html Using XEN_MAGIC macro instead of 0xf97cff8c : uint32_t selinux_magic = 0xf97cff8c; --> uint32_t xen_magic = XEN_MAGIC; Comment out the code(return 0 directly), if CONFIG_FLASK is not set.

v1: http://lists.xen.org/archives/html/xen-devel/2016-03/msg02430.html The first upstream patch to xen-devel mailing lists.

xen/arch/arm/bootfdt.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c index 8a14015..10d3382 100644 --- a/xen/arch/arm/bootfdt.c +++ b/xen/arch/arm/bootfdt.c @@ -163,6 +163,49 @@ static void __init process_memory_node(const void *fdt, int node, } }

+/**

• • check_xsm_signature - Check XSM Magic and Signature of the module header
• • A XSM module has a special header

• • ---

• • uint magic | uint target_len | uchar target[8] |
• • 0xf97cff8c | 8 | "XenFlask" |

• • ---

• • 0xf97cff8c is policy magic number (XSM_MAGIC).
• • So we only read the first 16 bytes of the module, then check these three
• • parts. This checking (memcmp) assumes little-endian byte order.
• */

+static bool __init check_xsm_signature(const void *fdt, int node,

•                                   const char *name,
  

•                                   u32 address_cells, u32 size_cells)
  

+{ +#ifdef CONFIG_FLASK

• u32 xen_magic = XSM_MAGIC, target_len = 8;
• const struct fdt_property *prop;
• unsigned char buff[16];
• paddr_t start, size;
• const __be32 *cell;
• int len;
• prop = fdt_get_property(fdt, node, "reg", &len);
• if ( !prop || len < dt_cells_to_size(address_cells + size_cells))

•    return 0;
  

• cell = (const __be32 *)prop->data;
• device_tree_get_reg(&cell, address_cells, size_cells, &start, &size);

I would prefer if you re-order the code in process_multiboot_node to get the base address and size first. This function will then only check if the signature is valid.

• copy_from_paddr(buff, start, sizeof(buff));
• if (memcmp(buff, (void *) &xen_magic, sizeof(u32)) ||

•    memcmp(buff + sizeof(u32), (void *) &target_len, sizeof(u32)) ||
  

•    memcmp(buff + sizeof(u32) * 2, "XenFlask", target_len))
  

Do we really need to test all those fields? The current check in xsm_policy.c only check the magic number.

Also I would prefer if you factor the code to copy/check in an helper and re-use it in xsm_dt_policy_init.

•    return 0;
  

• return 1;

+#else

• return 0;

+#endif +}

• static void __init process_multiboot_node(const void *fdt, int node, const char *name, u32 address_cells, u32 size_cells)

@@ -186,7 +229,13 @@ static void __init process_multiboot_node(const void *fdt, int node, else kind = BOOTMOD_UNKNOWN;

• /* Guess that first two unknown are kernel and ramdisk respectively. */

• /**

• * Guess the kind of these first two unknown respectively:
  

• * (1) The first unknown must be kernel;
  

• * (2) The second unknown is ramdisk, only if we have ramdisk;
  

• * (3) Start from the 2nd unknown, detect the XSM binary signature;
  

• * (4) If we got XSM in the 2nd unknown, that means we have not initrd.
  

s/not/no/

• */
  if ( kind == BOOTMOD_UNKNOWN )
  {
      switch ( kind_guess++ )
  

@@ -195,6 +244,9 @@ static void __init process_multiboot_node(const void *fdt, int node, case 1: kind = BOOTMOD_RAMDISK; break; default: break; }

•    if (kind_guess > 1 && check_xsm_signature(fdt, node, name,
  

•                                              address_cells, size_cells))
  

•        kind = BOOTMOD_XSM;
  }
  
  prop = fdt_get_property(fdt, node, "reg", &len);
  
  

Regards,