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Date: Mon, 25 Jan 2021 13:54:54 +0000
From: Marc Zyngier <maz@...nel.org>
To: Ard Biesheuvel <ardb@...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 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! ;-).
Thanks,
M.
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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