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Date: Thu, 5 May 2022 19:03:08 +0100 From: Mark Rutland <mark.rutland@....com> To: Sami Tolvanen <samitolvanen@...gle.com> Cc: LKML <linux-kernel@...r.kernel.org>, Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Joao Moreira <joao@...rdrivepizza.com>, Sedat Dilek <sedat.dilek@...il.com>, Steven Rostedt <rostedt@...dmis.org>, linux-hardening@...r.kernel.org, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, llvm@...ts.linux.dev Subject: Re: [RFC PATCH 10/21] treewide: Drop function_nocfi On Thu, May 05, 2022 at 09:51:39AM -0700, Sami Tolvanen wrote: > On Thu, May 5, 2022 at 9:30 AM Mark Rutland <mark.rutland@....com> wrote: > > I also believe that in most cases we can drop the __nocfi annotation on callers > > now that we can mark the called assembly function with SYM_TYPED_FUNC_START(). > > Good point, thanks for pointing that out. I'll add these to the next > version of the series. Also, I *think* we can drop __nocfi from __init, and always check calls to functions in .init.text. IIUC we made those __nocfi because it leads to section mismatches, and dangling entries in the jump tables after we discarded the init text, neither of which should be a problem with kCFI. Unfortuantely, that appears to be masking some existing type mismatches; e.g. psci_dt_init() blows up because it uses the wrong type for its callees (a mismatched `const`). With that fixed up, arm64 boots fine. > > There' a latent bug here with the existing CFI scheme, since > > `kpti_install_ng_mappings` isn't marked with __nocfi, and should explode when > > calling `idmap_kpti_install_ng_mappings` via the idmap. > > The CONFIG_UNMAP_KERNEL_AT_EL0 version of kpti_install_ng_mappings is > marked __nocfi Ah, so it is. Sorry for the noise! > > There' a latent bug here with the existing CFI scheme, since > > `machine_kexec` isn't marked with __nocfi, and should explode when calling > > `cpu_soft_restart` via the idmap. > > But it's indeed missing from this one. Cool; I'll prep a patch that fixes just this, then. Thanks, Mark.
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