2f27bf834e
When the policy for user space is to ignore misaligned accesses from user space, the processor then performs a documented rotation on the accessed data. This is the result of the access being trapped, and the kernel disabling the alignment trap before returning to user space again. In kernel space we always want misaligned accesses to be fixed up. This is enforced by always re-enabling the alignment trap on every entry into kernel space from user space. No such re-enabling is performed when an exception occurs while already in kernel space as the alignment trap is always supposed to be enabled in that case. There is however a small race window when a misaligned access in user space is trapped and the alignment trap disabled, but the CPU didn't return to user space just yet. Any exception would be entered from kernel space at that point and the kernel would then execute with the alignment trap disabled. Thanks to Maxime Bizon <mbizon@freebox.fr> for providing a test module that made this issue reproducible. Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> |
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