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Message-ID: <f6045fd9844f3b14c20bf86e60aa3a81253230cd.camel@linux.ibm.com>
Date: Mon, 02 Nov 2020 07:13:28 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Chester Lin <clin@...e.com>, Ard Biesheuvel <ardb@...nel.org>
Cc: James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
linux-efi <linux-efi@...r.kernel.org>,
linux-integrity <linux-integrity@...r.kernel.org>,
linux-security-module@...r.kernel.org, X86 ML <x86@...nel.org>,
"Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [PATCH v3 3/3] arm64/ima: add ima_arch support
On Mon, 2020-11-02 at 15:20 +0800, Chester Lin wrote:
> On Fri, Oct 30, 2020 at 12:53:25PM +0100, Ard Biesheuvel wrote:
> > On Fri, 30 Oct 2020 at 07:09, Chester Lin <clin@...e.com> wrote:
> > >
> > > Add arm64 IMA arch support. The code and arch policy is mainly inherited
> > > from x86.
> > >
> > > Signed-off-by: Chester Lin <clin@...e.com>
> > > ---
> > > arch/arm64/Kconfig | 1 +
> > > arch/arm64/kernel/Makefile | 2 ++
> > > arch/arm64/kernel/ima_arch.c | 43 ++++++++++++++++++++++++++++++++++++
> > > 3 files changed, 46 insertions(+)
> > > create mode 100644 arch/arm64/kernel/ima_arch.c
> > >
> > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > > index a42e8d13cc88..496a4a26afc6 100644
> > > --- a/arch/arm64/Kconfig
> > > +++ b/arch/arm64/Kconfig
> > > @@ -201,6 +201,7 @@ config ARM64
> > > select SWIOTLB
> > > select SYSCTL_EXCEPTION_TRACE
> > > select THREAD_INFO_IN_TASK
> > > + imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI
> > > help
> > > ARM 64-bit (AArch64) Linux support.
> > >
> > > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> > > index bbaf0bc4ad60..0f6cbb50668c 100644
> > > --- a/arch/arm64/kernel/Makefile
> > > +++ b/arch/arm64/kernel/Makefile
> > > @@ -69,3 +69,5 @@ extra-y += $(head-y) vmlinux.lds
> > > ifeq ($(CONFIG_DEBUG_EFI),y)
> > > AFLAGS_head.o += -DVMLINUX_PATH="\"$(realpath $(objtree)/vmlinux)\""
> > > endif
> > > +
> > > +obj-$(CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT) += ima_arch.o
> > > diff --git a/arch/arm64/kernel/ima_arch.c b/arch/arm64/kernel/ima_arch.c
> > > new file mode 100644
> > > index 000000000000..564236d77adc
> > > --- /dev/null
> > > +++ b/arch/arm64/kernel/ima_arch.c
> > > @@ -0,0 +1,43 @@
> > > +// SPDX-License-Identifier: GPL-2.0+
> > > +/*
> > > + * Copyright (C) 2018 IBM Corporation
> > > + */
> > > +#include <linux/efi.h>
> > > +#include <linux/module.h>
> > > +#include <linux/ima.h>
> > > +
> > > +bool arch_ima_get_secureboot(void)
> > > +{
> > > + static bool sb_enabled;
> > > + static bool initialized;
> > > +
> > > + if (!initialized & efi_enabled(EFI_BOOT)) {
> > > + sb_enabled = ima_get_efi_secureboot();
> > > + initialized = true;
> > > + }
> > > +
> > > + return sb_enabled;
> > > +}
> > > +
> > > +/* secure and trusted boot arch rules */
> > > +static const char * const sb_arch_rules[] = {
> > > +#if !IS_ENABLED(CONFIG_KEXEC_SIG)
> > > + "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig",
> > > +#endif /* CONFIG_KEXEC_SIG */
> > > + "measure func=KEXEC_KERNEL_CHECK",
> > > +#if !IS_ENABLED(CONFIG_MODULE_SIG)
> > > + "appraise func=MODULE_CHECK appraise_type=imasig",
> > > +#endif
> > > + "measure func=MODULE_CHECK",
> > > + NULL
> > > +};
> > > +
> > > +const char * const *arch_get_ima_policy(void)
> > > +{
> > > + if (IS_ENABLED(CONFIG_IMA_ARCH_POLICY) && arch_ima_get_secureboot()) {
> > > + if (IS_ENABLED(CONFIG_MODULE_SIG))
> > > + set_module_sig_enforced();
> > > + return sb_arch_rules;
> > > + }
> > > + return NULL;
> > > +}
> > > --
> > > 2.28.0
> > >
> >
> > Can we move all this stuff into security/integrity/ima/ima_efi.c instead?
> >
> Actually I hesitated to move all this stuff into ima_efi.c when coding v3
> because I haven't figured out a clear picture to achieve it. Since each
> architecture could still have different details to trigger secure boot detection
> and define their arch-specific rules [e.g. Having boot_params in x86_64 creates
> more conditions that need to be determined before calling get_sb_mode()], moving
> all this stuff seems to decrease the flexibility. Besides, it might also affect
> the consistency of ima_arch as well, for example, ppc and s390 still use these
> function prototypes defined in ima.h. Since these functions are already referred
> by non-EFI architectures, why don't we still reuse these prototypes? For example,
> we could remain a smaller arch_ima_get_secureboot() and the arch-specific rules
> but move the major part of arch_get_ima_policy() into ima_efi.c. For example,
> we could implement an efi_ima_policy() for arch_get_ima_policy() to call so that
> the arch_get_ima_policy() doesn't have to know some details such as checking
> conditions or calling set_module_sig_enforced().
>
> Please feel free to let me know if any suggestions.
Yes, that is the point and the reason for defining ima_efi.c and
conditionally including it only for EFI systems. The existing ppc and
s390 code should remain unaffected by this change.
thanks,
Mimi
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