Fix crash when user cancels Windows Hello dialog (nullptr from e.what()) - #202
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When exceptions cross the VTL0/VTL1 boundary, the exception object's message pointer can become nullptr because VTL0 heap memory is not accessible from VTL1. Calling std::string(e.what()) or strlen(e.what()) on a nullptr triggers an access violation that fast-fails the host process. This was reproducible with HostAppUserBound (Create Key -> Cancel) and HostAppUserBoundSignVerify (Sign -> Cancel) sample apps. Fix: Add a safe_what() helper in both userboundkey.vtl1.cpp (3 sites) and userboundkey.vtl0.cpp (5 sites) that returns a fallback string when e.what() is nullptr. Note: This is distinct from the fix in PR #201 which addressed incorrect HRESULT mapping of KeyCredentialStatus enum values. That fix ensured the cancel error is reported as a real failure HRESULT; this fix hardens the catch blocks that log the error before re-throwing. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Branden Bonaby (bbonaby)
approved these changes
Apr 22, 2026
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When exceptions cross the VTL0/VTL1 boundary, the exception object's message pointer can become nullptr because VTL0 heap memory is not accessible from VTL1. Calling std::string(e.what()) or strlen(e.what()) on a nullptr triggers an access violation that fast-fails the host process.
This was reproducible with HostAppUserBound (Create Key -> Cancel) and HostAppUserBoundSignVerify (Sign -> Cancel) sample apps.
Fix: Add a safe_what() helper in both userboundkey.vtl1.cpp (3 sites) and userboundkey.vtl0.cpp (5 sites) that returns a fallback string when e.what() is nullptr.
Note: This is distinct from the fix in PR #201 which addressed incorrect HRESULT mapping of KeyCredentialStatus enum values. That fix ensured the cancel error is reported as a real failure HRESULT; this fix hardens the catch blocks that log the error before re-throwing.