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We have a general signal fuzzer, sigfuz, which can modify the MSR & NIP before sigreturn. But the chance of it hitting a kernel address and also clearing MSR_PR is fairly slim. So add a specific test of sigreturn to a kernel address, both with and without attempting to clear MSR_PR (which the kernel must block). Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20211209115944.4062384-1-mpe@ellerman.id.au