riscv_syscall.S: Fix a massive bug in syscall dispatch logic #314
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
There is an enormous error in the system call dispatch logic; if a task is inside a critical section (local interrupts disabled) there is a chance that during a context switch when the task resumes, local interrupts are erroneously ENABLED. This obviously leads to unexpected crashes and such. This happens when the CPU status has Previous Interrupt Enable (PIE) set to 1, even though Interrupt Enable (IE) is set to 0. When the system call returns via ERET, the CPU sets PIE->IE and if PIE=1 interrupts get enabled. This is fixed easily by explicitly CLEARING PIE from the register save area, if IE=0 when the system call was started.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
There is an enormous error in the system call dispatch logic; if a task is inside a critical section (local interrupts disabled) there is a chance that during a context switch when the task resumes, local interrupts are erroneously ENABLED. This obviously leads to unexpected crashes and such.
This happens when the CPU status has Previous Interrupt Enable (PIE) set to 1, even though Interrupt Enable (IE) is set to 0.
When the system call returns via ERET, the CPU sets PIE->IE and if PIE=1 interrupts get enabled.
This is fixed easily by explicitly CLEARING PIE from the register save area, if IE=0 when the system call was started.
Backport from upstream