-
Petr Pavlu authored
The kprobes optimization check can_optimize() calls insn_is_indirect_jump() to detect indirect jump instructions in a target function. If any is found, creating an optprobe is disallowed in the function because the jump could be from a jump table and could potentially land in the middle of the target optprobe. With retpolines, insn_is_indirect_jump() additionally looks for calls to indirect thunks which the compiler potentially used to replace original jumps. This extra check is however unnecessary because jump tables are disabled when the kernel is built with retpolines. The same is currently the case with IBT. Based on this observation, remove the logic to look for calls to indirect thunks and skip the check for indirect jumps altogether if the kernel is built with retpolines or IBT. Remove subsequently the symbols __indirect_thunk_start and __indirect_thunk_end which are no longer needed. Dropping this logic indirectly fixes a problem where the range [__indirect_thunk_start, __indirect_thunk_end] wrongly included also the return thunk. It caused that machines which used the return thunk as a mitigation and didn't have it patched by any alternative ended up not being able to use optprobes in any regular function. Fixes: 0b53c374 ("x86/retpoline: Use -mfunction-return") Suggested-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Suggested-by:
Masami Hiramatsu (Google) <mhiramat@kernel.org> Signed-off-by:
Petr Pavlu <petr.pavlu@suse.com> Signed-off-by:
Borislav Petkov (AMD) <bp@alien8.de> Acked-by:
833fd800
