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X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi all, I'm occasionally seeing panics due to branch target exceptions when loading kernel modules when bti is enabled. It seems to happen when __init code calls into non __init code which happens to have been loaded a long way away, and so a module plt entry has been created. When the code for the module was generated, the call from init to non-init was through a direct branch, so no `bti c` was injected in the callee. I believe gcc needs to inject bti instructions due to those cross-section calls regardless of direct/indirect, so I've filed: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106671 for the issue, along with a little snippet that makes the same type of issue happen in user space. In the meantime, should we mark BTI_KERNEL as broken? or any other ideas on how to work around code generated without bti instructions like this? Enable the guard page attribute later? or try to keep init and non-init allocations close together? And then finally, here are the exact instructions that are causing me problems most frequently, from ipmi_si.ko: > Disassembly of section .init.text: > > 0000000000000000 : > ... snip ... > 158: 94000000 bl 0 > 158: R_AARCH64_CALL26 .text+0x13b4 > > Disassembly of section .text: > > 00000000000013b4 : > 13b4: d503201f nop > 13b8: d503201f nop > 13bc: d503233f paciasp Where the plt entry is injected at the call at init_module+0x158, and then the branch target exception happens at cleanup_ipmi_si.part.0+0x0. -- Scott _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel