Re: [PATCH 3/6] powerpc/64s: Patch barrier_nospec in modules

["Michal Suchánek" <msuchanek@suse.de>]

On Tue, 24 Apr 2018 14:15:56 +1000
Michael Ellerman <mpe@ellerman.id.au> wrote:

> From: Michal Suchanek <msuchanek@suse.de>
> 
> Note that unlike RFI which is patched only in kernel the nospec state
> reflects settings at the time the module was loaded.
> 
> Iterating all modules and re-patching every time the settings change
> is not implemented.
> 
> Based on lwsync patching.
> 
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
>  arch/powerpc/include/asm/setup.h  |  6 ++++++
>  arch/powerpc/kernel/module.c      |  6 ++++++
>  arch/powerpc/lib/feature-fixups.c | 16 +++++++++++++---
>  3 files changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/setup.h
> b/arch/powerpc/include/asm/setup.h index afc7280cce3b..4335cddc1cf2
> 100644 --- a/arch/powerpc/include/asm/setup.h
> +++ b/arch/powerpc/include/asm/setup.h
> @@ -54,6 +54,12 @@ void setup_rfi_flush(enum l1d_flush_type, bool
> enable); void do_rfi_flush_fixups(enum l1d_flush_type types);
>  void do_barrier_nospec_fixups(bool enable);
>  
> +#ifdef CONFIG_PPC_BOOK3S_64
> +void do_barrier_nospec_fixups_range(bool enable, void *start, void
> *end); +#else
> +static inline void do_barrier_nospec_fixups_range(bool enable, void
> *start, void *end) { }; +#endif
> +
>  #endif /* !__ASSEMBLY__ */
>  
>  #endif	/* _ASM_POWERPC_SETUP_H */
> diff --git a/arch/powerpc/kernel/module.c
> b/arch/powerpc/kernel/module.c index 3f7ba0f5bf29..a72698cd3dd0 100644
> --- a/arch/powerpc/kernel/module.c
> +++ b/arch/powerpc/kernel/module.c
> @@ -72,6 +72,12 @@ int module_finalize(const Elf_Ehdr *hdr,
>  		do_feature_fixups(powerpc_firmware_features,
>  				  (void *)sect->sh_addr,
>  				  (void *)sect->sh_addr +
> sect->sh_size); +
> +	sect = find_section(hdr, sechdrs, "__spec_barrier_fixup");
> +	if (sect != NULL)
> +		do_barrier_nospec_fixups_range(true,

This saves a global but always patches modules with the ORI
flush. The patching also produces a log message which can be confusing
to the user. Even when barrier is disabled "barrier-nospec: using ORI
speculation barrier" is logged when modules are loaded.

For consistency when debugging the settings I would suggest to keep the
export.

It is also no longer consistent with the commit message.

Thanks

Michal

> +				  (void *)sect->sh_addr,
> +				  (void *)sect->sh_addr +
> sect->sh_size); #endif
>  
>  	sect = find_section(hdr, sechdrs, "__lwsync_fixup");
> diff --git a/arch/powerpc/lib/feature-fixups.c
> b/arch/powerpc/lib/feature-fixups.c index 093c1d2ea5fd..3b37529f82f8
> 100644 --- a/arch/powerpc/lib/feature-fixups.c
> +++ b/arch/powerpc/lib/feature-fixups.c
> @@ -163,14 +163,14 @@ void do_rfi_flush_fixups(enum l1d_flush_type
> types) : "unknown");
>  }
>  
> -void do_barrier_nospec_fixups(bool enable)
> +void do_barrier_nospec_fixups_range(bool enable, void *fixup_start,
> void *fixup_end) {
>  	unsigned int instr, *dest;
>  	long *start, *end;
>  	int i;
>  
> -	start = PTRRELOC(&__start___barrier_nospec_fixup),
> -	end = PTRRELOC(&__stop___barrier_nospec_fixup);
> +	start = fixup_start;
> +	end = fixup_end;
>  
>  	instr = 0x60000000; /* nop */
>  
> @@ -189,6 +189,16 @@ void do_barrier_nospec_fixups(bool enable)
>  	printk(KERN_DEBUG "barrier-nospec: patched %d locations\n",
> i); }
>  
> +void do_barrier_nospec_fixups(bool enable)
> +{
> +	void *start, *end;
> +
> +	start = PTRRELOC(&__start___barrier_nospec_fixup),
> +	end = PTRRELOC(&__stop___barrier_nospec_fixup);
> +
> +	do_barrier_nospec_fixups_range(enable, start, end);
> +}
> +
>  #endif /* CONFIG_PPC_BOOK3S_64 */
>  
>  void do_lwsync_fixups(unsigned long value, void *fixup_start, void
> *fixup_end)