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The rtas system call handler sys_rtas() delegates certain input validation steps to a helper function: block_rtas_call(). One of these steps ensures that the user-supplied token value maps to a known RTAS function. This is done by performing a "reverse" token-to-function lookup via rtas_token_to_function_untrusted() to obtain an rtas_function object. In changes to come, sys_rtas() itself will need the function descriptor for the token. To prepare: * Move the lookup and validation up into sys_rtas() and pass the resulting rtas_function pointer to block_rtas_call(), which is otherwise unconcerned with the token value. * Change block_rtas_call() to report the RTAS function name instead of the token value on validation failures, since it can now rely on having a valid function descriptor. One behavior change is that sys_rtas() now silently errors out when passed a bad token, before calling block_rtas_call(). So we will no longer log "RTAS call blocked - exploit attempt?" on invalid tokens. This is consistent with how sys_rtas() currently handles other "metadata" (nargs and nret), while block_rtas_call() is primarily concerned with validating the arguments to be passed to specific RTAS functions. 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-v6-5-e9eafd0c8c6c@linux.ibm.com |
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