Fix IAR warning about volatile access

[embhorn]

Description

Read the volatile once into a local copy, then use the copy in expressions — satisfying IAR's stricter volatile access rules. "undefined behavior: the order of volatile accesses is undefined in this statement"

Fixes zd21385

Testing

Customer confirmed clean build with IAR tools

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation

[Copilot]

Pull request overview

Updates RSA unpadding and ticket decryption error masking to satisfy IAR’s stricter rules around volatile access by first reading volatile values into local copies and using those in subsequent expressions.

Changes:

• Refactored constant-time RSA unpadding checks to use local copies of volatile variables in expressions.
• Updated ticket encryption callback RSA path to use a local copy of a volatile mask when composing lastErr.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
wolfcrypt/src/rsa.c	Reads volatile masking state into local temporaries before combining/deriving masks to avoid IAR volatile-use warnings.
src/internal.c	Uses a local copy of lenErrMask when building args->lastErr to avoid volatile access in compound expressions.

Comments suppressed due to low confidence (2)

src/internal.c:1

• Since lenErrMaskCopy is the value actually used in subsequent expressions, computing directly into the non-volatile local (and only keeping volatile if it’s required for the toolchain workaround) would reduce noise and avoid an extra volatile write+read pair. For example, compute the mask into lenErrMaskCopy and use that consistently.
  src/internal.c:1
• Since lenErrMaskCopy is the value actually used in subsequent expressions, computing directly into the non-volatile local (and only keeping volatile if it’s required for the toolchain workaround) would reduce noise and avoid an extra volatile write+read pair. For example, compute the mask into lenErrMaskCopy and use that consistently.

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[embhorn]

Jenkins retest this please

[dgarske]

These changes feel "hacky". Perhaps they need "volatile" added? I liked the original code better. Can we have IAR ignore that specific warning?

[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #10045

Scan targets checked: src, src-bugs, src-compliance, wolfcrypt-bugs, wolfcrypt-src

No new issues found in the changed files. ✅

[embhorn]

These changes feel "hacky". Perhaps they need "volatile" added? I liked the original code better. Can we have IAR ignore that specific warning?

The issue is about multiple volatile statements on one line, and the warning is valid.
I changed the logic a bit and I think this new approach is better and more clear.