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Date: Fri, 24 Jun 2022 15:09:03 +0200 From: Ard Biesheuvel <ardb@...nel.org> To: Will Deacon <will@...nel.org> Cc: Linux ARM <linux-arm-kernel@...ts.infradead.org>, linux-hardening@...r.kernel.org, Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>, Kees Cook <keescook@...omium.org>, Catalin Marinas <catalin.marinas@....com>, Mark Brown <broonie@...nel.org>, Anshuman Khandual <anshuman.khandual@....com> Subject: Re: [PATCH v4 19/26] arm64: kaslr: defer initialization to late initcall where permitted On Fri, 24 Jun 2022 at 15:08, Will Deacon <will@...nel.org> wrote: > > On Mon, Jun 13, 2022 at 04:45:43PM +0200, Ard Biesheuvel wrote: > > The early KASLR init code runs extremely early, and anything that could > > be deferred until later should be. So let's defer the randomization of > > the module region until much later - this also simplifies the > > arithmetic, given that we no longer have to reason about the link time > > vs load time placement of the core kernel explicitly. Also get rid of > > the global status variable, and infer the status reported by the > > diagnostic print from other KASLR related context. > > > > While at it, get rid of the special case for KASAN without > > KASAN_VMALLOC, which never occurs in practice. > > > > Signed-off-by: Ard Biesheuvel <ardb@...nel.org> > > --- > > arch/arm64/kernel/kaslr.c | 95 +++++++++----------- > > 1 file changed, 40 insertions(+), 55 deletions(-) > > [...] > > > @@ -163,33 +169,12 @@ u64 __init kaslr_early_init(void) > > * when ARM64_MODULE_PLTS is enabled. > > */ > > module_range = MODULES_VSIZE - (u64)(_etext - _stext); > > - module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; > > } > > > > /* use the lower 21 bits to randomize the base of the module region */ > > module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; > > module_alloc_base &= PAGE_MASK; > > > > - return offset; > > -} > > - > > -static int __init kaslr_init(void) > > -{ > > - switch (kaslr_status) { > > - case KASLR_ENABLED: > > - pr_info("KASLR enabled\n"); > > - break; > > - case KASLR_DISABLED_CMDLINE: > > - pr_info("KASLR disabled on command line\n"); > > - break; > > - case KASLR_DISABLED_NO_SEED: > > - pr_warn("KASLR disabled due to lack of seed\n"); > > - break; > > - case KASLR_DISABLED_FDT_REMAP: > > - pr_warn("KASLR disabled due to FDT remapping failure\n"); > > - break; > > - } > > - > > return 0; > > } > > -core_initcall(kaslr_init) > > +late_initcall(kaslr_init) > > Are you sure this isn't too late? I'm nervous that we might have called > request_module() off the back of all the other initcalls that we've run by > this point. > Yeah, I just realized the other day that this is probably too late. subsys_initcall() might be more suitable here
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