Update EVP cipher APIs to gracefully handle null EVP_CIPHER_CTX

[andrewhop]

Issues:

Resolves V1187459157

Description of changes:

This change does 3 things:

1. All EVP_CIPHER_CTX now start off as poisoned and require calling EVP_CipherInit_ex to cure it
2. All EVP Encrypt/Decrypt Update/Final now check that the EVP_CIPHER_CTX and EVP_CIPHER_CTX->cipher are not null
3. Add the start of reusable safety macros inspired by s2n-tls

Call-outs:

This is an alternative approach to #1420.

The __AWS_LC_ENSURE macro uses the do {} while (0) trick to ensure the action is run once, anything passed into the macro doesn't accidentally expand and change the scope, and the compiler enforces you add a ; after the macro. We use this trick in other macros and all compilers are smart enough to optimize out the jump.

Testing:

GUARD_PTR(ctx); expands to:

  do {
    if (!((ctx) != ((void *)0))) {
      ERR_put_error(ERR_LIB_CRYPTO, 0, (3 | 64), "_file_name_", 259);
      return 0;
    }
  } while (0);

Here is an example with the macro, and here it is implemented as a traditional if/else. Both result in the same code.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.19%. Comparing base (c5d38a5) to head (4c0a39b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1398   +/-   ##
=======================================
  Coverage   77.18%   77.19%           
=======================================
  Files         426      426           
  Lines       71449    71465   +16     
=======================================
+ Hits        55146    55165   +19     
+ Misses      16303    16300    -3     

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[nebeid]

Why there are no guards for CipherInit_ex, CipherUpdate and CipherFinal_ex? ctx is accessed there right away.

[nebeid]

I still see CipherInit_ex not having a GUARD_PTR, is there a reason for that?

aws-lc/crypto/fipsmodule/cipher/cipher.c

Line 142 in 4c0a39b

int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *cipher,