powerpc/rtas: Avoid warning on invalid token argument to sys_rtas()
rtas_token_to_function() WARNs when passed an invalid token; it's meant to catch bugs in kernel-based users of RTAS functions. However, user space controls the token value passed to rtas_token_to_function() by block_rtas_call(), so user space with sufficient privilege to use sys_rtas() can trigger the warnings at will: unexpected failed lookup for token 2048 WARNING: CPU: 20 PID: 2247 at arch/powerpc/kernel/rtas.c:556 rtas_token_to_function+0xfc/0x110 ... NIP rtas_token_to_function+0xfc/0x110 LR rtas_token_to_function+0xf8/0x110 Call Trace: rtas_token_to_function+0xf8/0x110 (unreliable) sys_rtas+0x188/0x880 system_call_exception+0x268/0x530 system_call_common+0x160/0x2c4 It's desirable to continue warning on bogus tokens in rtas_token_to_function(). Currently it is used to look up RTAS function descriptors when tracing, where we know there has to have been a successful descriptor lookup by different means already, and it would be a serious inconsistency for the reverse lookup to fail. So instead of weakening rtas_token_to_function()'s contract by removing the warnings, introduce rtas_token_to_function_untrusted(), which has no opinion on failed lookups. Convert block_rtas_call() and rtas_token_to_function() to use it. Fixes: 8252b882 ("powerpc/rtas: improve function information lookups") Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231212-papr-sys_rtas-vs-lockdown-v6-1-e9eafd0c8c6c@linux.ibm.com
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