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Message-ID: <CAMj1kXGTu8AtMnm7NxB8M2xFuXHSKzAx2hjjeaAW2v-usvavVQ@mail.gmail.com>
Date: Mon, 25 Jan 2021 15:19:30 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Marc Zyngier <maz@...nel.org>
Cc: Linux ARM <linux-arm-kernel@...ts.infradead.org>,
kvmarm <kvmarm@...ts.cs.columbia.edu>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Mark Rutland <mark.rutland@....com>,
David Brazdil <dbrazdil@...gle.com>,
Alexandru Elisei <alexandru.elisei@....com>,
Jing Zhang <jingzhangos@...gle.com>,
Ajay Patil <pajay@....qualcomm.com>,
Prasad Sodagudi <psodagud@...eaurora.org>,
Srinivas Ramana <sramana@...eaurora.org>,
James Morse <james.morse@....com>,
Julien Thierry <julien.thierry.kdev@...il.com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v5 18/21] arm64: Move "nokaslr" over to the early
cpufeature infrastructure
On Mon, 25 Jan 2021 at 14:54, Marc Zyngier <maz@...nel.org> wrote:
>
> On 2021-01-25 12:54, Ard Biesheuvel wrote:
> > On Mon, 25 Jan 2021 at 11:53, Marc Zyngier <maz@...nel.org> wrote:
> >>
> >> Given that the early cpufeature infrastructure has borrowed quite
> >> a lot of code from the kaslr implementation, let's reimplement
> >> the matching of the "nokaslr" option with it.
> >>
> >> Signed-off-by: Marc Zyngier <maz@...nel.org>
> >> Acked-by: Catalin Marinas <catalin.marinas@....com>
> >> Acked-by: David Brazdil <dbrazdil@...gle.com>
> >> ---
> >> arch/arm64/kernel/idreg-override.c | 15 +++++++++++++
> >> arch/arm64/kernel/kaslr.c | 36
> >> ++----------------------------
> >> 2 files changed, 17 insertions(+), 34 deletions(-)
> >>
> >> diff --git a/arch/arm64/kernel/idreg-override.c
> >> b/arch/arm64/kernel/idreg-override.c
> >> index cbb8eaa48742..3ccf51b84ba4 100644
> >> --- a/arch/arm64/kernel/idreg-override.c
> >> +++ b/arch/arm64/kernel/idreg-override.c
> >> @@ -31,8 +31,22 @@ static const struct ftr_set_desc mmfr1 __initdata =
> >> {
> >> },
> >> };
> >>
> >> +extern struct arm64_ftr_override kaslr_feature_override;
> >> +
> >> +static const struct ftr_set_desc kaslr __initdata = {
> >
> > This should be __initconst not __initdata (below too)
> >
> >> + .name = "kaslr",
> >> +#ifdef CONFIG_RANDOMIZE_BASE
> >> + .override = &kaslr_feature_override,
> >> +#endif
> >> + .fields = {
> >> + { "disabled", 0 },
> >> + {}
> >> + },
> >> +};
> >> +
> >> static const struct ftr_set_desc * const regs[] __initdata = {
> >> &mmfr1,
> >> + &kaslr,
> >> };
> >>
> >> static const struct {
> >> @@ -41,6 +55,7 @@ static const struct {
> >> } aliases[] __initdata = {
> >> { "kvm-arm.mode=nvhe", "id_aa64mmfr1.vh=0" },
> >> { "kvm-arm.mode=protected", "id_aa64mmfr1.vh=0" },
> >> + { "nokaslr", "kaslr.disabled=1" },
> >> };
> >>
> >
> > This struct now takes up
> > - ~100 bytes for the characters themselves (which btw are not emitted
> > into __initdata or __initconst)
> > - 6x8 bytes for the char pointers
> > - 6x24 bytes for the RELA relocations that annotate these pointers as
> > quantities that need to be relocated at boot (on a kernel built with
> > KASLR)
> >
> > I know it's only a drop in the ocean, but in this case, where the
> > struct is statically declared and defined only once, and in the same
> > place, we could easily turn this into
> >
> > static const struct {
> > char alias[24];
> > char param[20];
> > };
> >
> > and get rid of all the overhead. The only slightly annoying thing is
> > that the array sizes need to be kept in sync with the largest instance
> > appearing in the array, but this is easy when the struct type is
> > declared in the same place where its only instance is defined.
>
> Fair enough. I personally find the result butt-ugly, but I agree
> that it certainly saves some memory. Does the following work for
> you? I can even give symbolic names to the various constants (how
> generous of me! ;-).
>
To be honest, I was anticipating more of a discussion, but this looks
reasonable to me. Does 'char feature[80];' really need 80 bytes
though?
> diff --git a/arch/arm64/kernel/idreg-override.c
> b/arch/arm64/kernel/idreg-override.c
> index d1310438d95c..9e7043bdc808 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -14,15 +14,15 @@
> #include <asm/setup.h>
>
> struct ftr_set_desc {
> - const char *name;
> + char name[20];
> struct arm64_ftr_override *override;
> struct {
> - const char *name;
> + char name[20];
> u8 shift;
> } fields[];
> };
>
> -static const struct ftr_set_desc mmfr1 __initdata = {
> +static const struct ftr_set_desc mmfr1 __initconst = {
> .name = "id_aa64mmfr1",
> .override = &id_aa64mmfr1_override,
> .fields = {
> @@ -31,7 +31,7 @@ static const struct ftr_set_desc mmfr1 __initdata = {
> },
> };
>
> -static const struct ftr_set_desc pfr1 __initdata = {
> +static const struct ftr_set_desc pfr1 __initconst = {
> .name = "id_aa64pfr1",
> .override = &id_aa64pfr1_override,
> .fields = {
> @@ -40,7 +40,7 @@ static const struct ftr_set_desc pfr1 __initdata = {
> },
> };
>
> -static const struct ftr_set_desc isar1 __initdata = {
> +static const struct ftr_set_desc isar1 __initconst = {
> .name = "id_aa64isar1",
> .override = &id_aa64isar1_override,
> .fields = {
> @@ -54,7 +54,7 @@ static const struct ftr_set_desc isar1 __initdata = {
>
> extern struct arm64_ftr_override kaslr_feature_override;
>
> -static const struct ftr_set_desc kaslr __initdata = {
> +static const struct ftr_set_desc kaslr __initconst = {
> .name = "kaslr",
> #ifdef CONFIG_RANDOMIZE_BASE
> .override = &kaslr_feature_override,
> @@ -65,7 +65,7 @@ static const struct ftr_set_desc kaslr __initdata = {
> },
> };
>
> -static const struct ftr_set_desc * const regs[] __initdata = {
> +static const struct ftr_set_desc * const regs[] __initconst = {
> &mmfr1,
> &pfr1,
> &isar1,
> @@ -73,9 +73,9 @@ static const struct ftr_set_desc * const regs[]
> __initdata = {
> };
>
> static const struct {
> - const char *alias;
> - const char *feature;
> -} aliases[] __initdata = {
> + char alias[30];
> + char feature[80];
> +} aliases[] __initconst = {
> { "kvm-arm.mode=nvhe", "id_aa64mmfr1.vh=0" },
> { "kvm-arm.mode=protected", "id_aa64mmfr1.vh=0" },
> { "arm64.nobti", "id_aa64pfr1.bt=0" },
>
> --
> Jazz is not dead. It just smells funny...
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