[PATCH v2 2/3] powerpc/fsl: Add barrier_nospec implementation for NXP PowerPC Book3E

[Diana Madalina Craciun]

Hi Michael,

Thank you for the review.

On 07/03/2018 10:26 AM, Michael Ellerman wrote:
> Hi Diana,
>
> A few comments below ...
>
> Diana Craciun <diana.craciun at nxp.com> writes:
>> Implement the barrier_nospec as a isync;sync instruction sequence.
>> The implementation uses the infrastructure built for BOOK3S 64.
> Do you have any details on why that sequence functions as an effective
> barrier on your chips?

It was recommended by the hardware team, I do not have details.

>
> In a lot of places we have eg:
>
>  +#if defined(CONFIG_PPC_BOOK3S_64) || defined(CONFIG_PPC_FSL_BOOK3E)
>
> Can you please add a Kconfig symbol to capture that. eg.
>
> config PPC_NOSPEC
> 	bool
>         default y
> 	depends on PPC_BOOK3S_64 || PPC_FSL_BOOK3E
>
>
> And then use that everywhere.

OK.

>
>> diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
>> index f67b3f6..405d572 100644
>> --- a/arch/powerpc/include/asm/barrier.h
>> +++ b/arch/powerpc/include/asm/barrier.h
>> @@ -86,6 +86,16 @@ do {									\
>>  // This also acts as a compiler barrier due to the memory clobber.
>>  #define barrier_nospec() asm (stringify_in_c(barrier_nospec_asm) ::: "memory")
>>  
>> +#elif defined(CONFIG_PPC_FSL_BOOK3E)
>> +/*
>> + * Prevent the execution of subsequent instructions speculatively using a
>> + * isync;sync instruction sequence.
>> + */
>> +#define barrier_nospec_asm NOSPEC_BARRIER_FIXUP_SECTION; nop; nop
>> +
>> +// This also acts as a compiler barrier due to the memory clobber.
>> +#define barrier_nospec() asm (stringify_in_c(barrier_nospec_asm) ::: "memory")
>> +
>>  #else /* !CONFIG_PPC_BOOK3S_64 */
>>  #define barrier_nospec_asm
>>  #define barrier_nospec()
> If we have CONFIG_PPC_NOSPEC this can be done something like:
>
> #ifdef CONFIG_PPC_BOOK3S_64
> #define NOSPEC_BARRIER_SLOT	nop
> #elif defined(CONFIG_PPC_FSL_BOOK3E)
> #define NOSPEC_BARRIER_SLOT	nop; nop
> #endif /* CONFIG_PPC_BOOK3S_64 */
>
> #ifdef CONFIG_PPC_NOSPEC
> /*
>  * Prevent execution of subsequent instructions until preceding branches have
>  * been fully resolved and are no longer executing speculatively.
>  */
> #define barrier_nospec_asm NOSPEC_BARRIER_FIXUP_SECTION; NOSPEC_BARRIER_SLOT
>
> // This also acts as a compiler barrier due to the memory clobber.
> #define barrier_nospec() asm (stringify_in_c(barrier_nospec_asm) ::: "memory")
> #else
> #define barrier_nospec_asm
> #define barrier_nospec()
> #endif /* CONFIG_PPC_NOSPEC */

OK.

>
>
>> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
>> index 2b4c40b2..d9dee43 100644
>> --- a/arch/powerpc/kernel/Makefile
>> +++ b/arch/powerpc/kernel/Makefile
>> @@ -76,7 +76,7 @@ endif
>>  obj64-$(CONFIG_HIBERNATION)	+= swsusp_asm64.o
>>  obj-$(CONFIG_MODULES)		+= module.o module_$(BITS).o
>>  obj-$(CONFIG_44x)		+= cpu_setup_44x.o
>> -obj-$(CONFIG_PPC_FSL_BOOK3E)	+= cpu_setup_fsl_booke.o
>> +obj-$(CONFIG_PPC_FSL_BOOK3E)	+= cpu_setup_fsl_booke.o security.o
>>  obj-$(CONFIG_PPC_DOORBELL)	+= dbell.o
>>  obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
> Can we instead do:
>
> obj-$(CONFIG_PPC_NOSPEC)	+= security.o

OK

>
>> diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
>> index c55e102..797c975 100644
>> --- a/arch/powerpc/kernel/security.c
>> +++ b/arch/powerpc/kernel/security.c
>> @@ -13,7 +13,9 @@
>>  #include <asm/setup.h>
>>  
>>  
>> +#ifdef CONFIG_PPC_BOOK3S_64
>>  unsigned long powerpc_security_features __read_mostly = SEC_FTR_DEFAULT;
>> +#endif /* CONFIG_PPC_BOOK3S_64 */
> Why are you making that book3s specific?
>
> By doing that you then can't use the existing versions of
> setup_barrier_nospec() and cpu_show_spectre_v1/v2().
>
>> @@ -24,6 +26,7 @@ static void enable_barrier_nospec(bool enable)
>>  	do_barrier_nospec_fixups(enable);
>>  }
>>  
>> +#ifdef CONFIG_PPC_BOOK3S_64
>>  void setup_barrier_nospec(void)
>>  {
>>  	bool enable;
>> @@ -46,6 +49,15 @@ void setup_barrier_nospec(void)
>>  	if (!no_nospec)
>>  		enable_barrier_nospec(enable);
>>  }
>> +#endif /* CONFIG_PPC_BOOK3S_64 */
>> +
>> +#ifdef CONFIG_PPC_FSL_BOOK3E
>> +void setup_barrier_nospec(void)
>> +{
>> +	if (!no_nospec)
>> +		enable_barrier_nospec(true);
>> +}
>> +#endif /* CONFIG_PPC_FSL_BOOK3E */
> eg. that is identical to the existing version except for the feature check:
>
> 	enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) &&
> 		 security_ftr_enabled(SEC_FTR_BNDS_CHK_SPEC_BAR);
>
>
> Both those bits are enabled by default, so you shouldn't need to elide
> that check.
>
> So basically you should be able to use the existing
> setup_barrier_nospec() if you just remove the ifdef around
> powerpc_security_features. Or am I missing something?

OK. I was under the impression that those bits are not enabled by
default. But obviously I was wrong. In this case I will use the existing
function.

>
>
>> diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
>> index 7445748..80c1e6e 100644
>> --- a/arch/powerpc/kernel/setup_32.c
>> +++ b/arch/powerpc/kernel/setup_32.c
>> @@ -116,6 +116,11 @@ notrace void __init machine_init(u64 dt_ptr)
>>  	/* Do some early initialization based on the flat device tree */
>>  	early_init_devtree(__va(dt_ptr));
>>  
>> +	/* Apply the speculation barrier fixup */
>> +#ifdef CONFIG_PPC_FSL_BOOK3E
>> +	setup_barrier_nospec();
>> +#endif
> This ifdef should be handled in a header with an empty version for the
> #else case.

OK

>
>> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
>> index 7a7ce8a..b2a644a 100644
>> --- a/arch/powerpc/kernel/setup_64.c
>> +++ b/arch/powerpc/kernel/setup_64.c
>> @@ -327,6 +327,12 @@ void __init early_setup(unsigned long dt_ptr)
>>  
>>  	/* Apply all the dynamic patching */
>>  	apply_feature_fixups();
>> +
>> +	/* Apply the speculation barrier fixup */
>> +#ifdef CONFIG_PPC_FSL_BOOK3E
>> +	setup_barrier_nospec();
>> +#endif /* CONFIG_PPC_FSL_BOOK3E */
> Can you call it from ppc_md->setup_arch() like the other platforms?
>
> Failing that we could put it in setup_arch() after the call to
> ppc_md->setup_arch(), so we can share it with powernv/pseries.

The reason for which I did not call it from the ppc_md->setup_arch() was
that from my point of view the mitigation is not specific to the
platform code, but rather to the CPU.

>
>> diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c
>> index 2b9173d..bea2b87 100644
>> --- a/arch/powerpc/lib/feature-fixups.c
>> +++ b/arch/powerpc/lib/feature-fixups.c
>> @@ -188,7 +188,40 @@ void do_barrier_nospec_fixups_range(bool enable, void *fixup_start, void *fixup_
>>  
>>  	printk(KERN_DEBUG "barrier-nospec: patched %d locations\n", i);
>>  }
>> +#endif /* CONFIG_PPC_BOOK3S_64 */
>> +
>> +#ifdef CONFIG_PPC_FSL_BOOK3E
>> +void do_barrier_nospec_fixups_range(bool enable, void *fixup_start, void *fixup_end)
>> +{
>> +	unsigned int instr[2], *dest;
>> +	long *start, *end;
>> +	int i;
>> +
>> +	start = fixup_start;
>> +	end = fixup_end;
>> +
>> +	instr[0] = PPC_INST_NOP;
>> +	instr[1] = PPC_INST_NOP;
>> +
>> +	if (enable) {
>> +		pr_info("barrier_nospec; using isync; sync as a speculation barrier\n");
>> +		instr[0] = PPC_INST_ISYNC;
>> +		instr[1] = PPC_INST_SYNC;
>> +	}
>> +
>> +	for (i = 0; start < end; start++, i++) {
>> +		dest = (void *)start + *start;
>> +		pr_devel("patching dest %lx\n", (unsigned long)dest);
>>  
>> +		patch_instruction(dest, instr[0]);
>> +		patch_instruction(dest + 1, instr[1]);
>> +	}
>> +
>> +	pr_debug("barrier-nospec: patched %d locations\n", i);
>> +}
>> +#endif /* CONFIG_PPC_FSL_BOOK3E */
> It's a bit unfortunate that we end up with two versions of that, which
> are 80% the same. But merging them without ugly ifdefs would require a
> bit more refactoring. So I guess it's OK for now.
>
> cheers
>
Regards,

Diana