Improve FWU documentation

 - Clarify the documentation of the 'FWU_SMC_IMAGE_COPY' SMC in the
   Firmware Update guide. Also extend the list of pre-conditions to
   include the additional input validation implemented by previous
   patches.

 - Improve documentation of bl1_plat_mem_check() in the porting
   guide. It now specifies that the generic FWU code protects
   bl1_plat_mem_check() from integer overflows resulting from
   the addition of the base address and size passed in arguments.

Change-Id: I07b47a3778df7b9c089529b2dd2135707640a91c
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/docs/porting-guide.md b/docs/porting-guide.md
index a74966c3..e8486f12 100644
--- a/docs/porting-guide.md
+++ b/docs/porting-guide.md
@@ -1121,10 +1121,15 @@ The default implementation spins forever.
                unsigned int flags
     Return   : int
 
-BL1 calls this function while handling FWU copy and authenticate SMCs. The
-platform must ensure that the provided `mem_base` and `mem_size` are mapped into
-BL1, and that this memory corresponds to either a secure or non-secure memory
-region as indicated by the security state of the `flags` argument.
+BL1 calls this function while handling FWU related SMCs, more specifically when
+copying or authenticating an image. Its responsibility is to ensure that the
+region of memory identified by `mem_base` and `mem_size` is mapped in BL1, and
+that this memory corresponds to either a secure or non-secure memory region as
+indicated by the security state of the `flags` argument.
+
+This function can safely assume that the value resulting from the addition of
+`mem_base` and `mem_size` fits into a `uintptr_t` type variable and does not
+overflow.
 
 This function must return 0 on success, a non-null error code otherwise.