Hi Marc,

On Mon, Feb 08, 2021 at 09:57:09AM +0000, Marc Zyngier wrote:

It recently came to light that there is a need to be able to override
some CPU features very early on, before the kernel is fully up and
running. The reasons for this range from specific feature support
(such as using Protected KVM on VHE HW, which is the main motivation
for this work) to errata workaround (a feature is broken on a CPU and
needs to be turned off, or rather not enabled).

This series tries to offer a limited framework for this kind of
problems, by allowing a set of options to be passed on the
command-line and altering the feature set that the cpufeature
subsystem exposes to the rest of the kernel. Note that this doesn't
change anything for code that directly uses the CPU ID registers.

I applied this locally, but I'm seeing consistent boot failure under QEMU when
KASAN is enabled. I tried sprinkling some __no_sanitize_address annotations
around (see below) but it didn't help. The culprit appears to be
early_fdt_map(), but looking a bit more closely, I'm really nervous about the
way we call into C functions from __primary_switched. Remember -- this code
runs _twice_ when KASLR is active: before and after the randomization. This
also means that any memory writes the first time around can be lost due to
the D-cache invalidation when (re-)creating the kernel page-tables.

Will

--->8

diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index dffb16682330..751ed55261b5 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c

@@ -195,7 +195,7 @@ static __init void parse_cmdline(void)
 /* Keep checkers quiet */
 void init_feature_override(void);
 
-asmlinkage void __init init_feature_override(void)
+asmlinkage void __init __no_sanitize_address init_feature_override(void)
 {
        int i;
 

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index 61845c0821d9..33581de05d2e 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c

@@ -170,12 +170,12 @@ static void __init smp_build_mpidr_hash(void)
 
 static void *early_fdt_ptr __initdata;
 
-void __init *get_early_fdt_ptr(void)
+void __init __no_sanitize_address *get_early_fdt_ptr(void)
 {
        return early_fdt_ptr;
 }
 
-asmlinkage void __init early_fdt_map(u64 dt_phys)
+asmlinkage void __init __no_sanitize_address early_fdt_map(u64 dt_phys)
 {
        int fdt_size;
 

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