icp: Use explicit_memset() exclusively in gcm_clear_ctx()

d634d20 fixed an information leak issue
where GCC's optimization passes had removed `memset()` operations meant
to sanitize sensitive data before memory is freed for use by the rest of
the kernel.

When I wrote it, I had assumed that the compiler would not remove the
other `memset()` operations, but upon reflection, I have realized that
this was a bad assumption to make. I would rather have a very slight
amount of additional overhead when calling `gcm_clear_ctx()` than risk a
future compiler remove `memset()` calls. This is likely to happen if
someone decides to try doing link time optimization and the person will
not think to audit the assembly output for issues like this, so it is
best to preempt the possibility before it happens.

Signed-off-by: Richard Yao <[email protected]>

Author: ryao

module/icp/algs/modes/modes.c

@@ -173,12 +173,12 @@ gcm_clear_ctx(gcm_ctx_t *ctx)
 #if defined(CAN_USE_GCM_ASM)
 	if (ctx->gcm_use_avx == B_TRUE) {
 		ASSERT3P(ctx->gcm_Htable, !=, NULL);
-		memset(ctx->gcm_Htable, 0, ctx->gcm_htab_len);
+		explicit_memset(ctx->gcm_Htable, 0, ctx->gcm_htab_len);
 		kmem_free(ctx->gcm_Htable, ctx->gcm_htab_len);
 	}
 #endif
 	if (ctx->gcm_pt_buf != NULL) {
-		memset(ctx->gcm_pt_buf, 0, ctx->gcm_pt_buf_len);
+		explicit_memset(ctx->gcm_pt_buf, 0, ctx->gcm_pt_buf_len);
 		vmem_free(ctx->gcm_pt_buf, ctx->gcm_pt_buf_len);
 	}
 	/* Optional */