Make ARM64_MODULE_PLTS a selectable Kconfig symbol, since some people
might have very big modules spilling out of the dedicated module area
into vmalloc. Help text is copied from the ARM 32-bit counterpart and
modified to a mention of KASLR and specific ARM errata workaround(s).
Signed-off-by: Florian Fainelli <[email protected]>
---
Changes in v3:
- take out the part about "The modules will use slightly more memory, but after
rounding up to page size, the actual memory footprint is usually the same.
- take out the "If unusure say Y", since we would really prefer this to
be off by default for maximum performance
Changes in v2:
- added Ard's paragraph about KASLR
- added a paragraph about specific workarounds also requiring
ARM64_MODULE_PLTS
arch/arm64/Kconfig | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 697ea0510729..9206feaeff07 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1418,8 +1418,26 @@ config ARM64_SVE
KVM in the same kernel image.
config ARM64_MODULE_PLTS
- bool
+ bool "Use PLTs to allow module memory to spill over into vmalloc area"
select HAVE_MOD_ARCH_SPECIFIC
+ help
+ Allocate PLTs when loading modules so that jumps and calls whose
+ targets are too far away for their relative offsets to be encoded
+ in the instructions themselves can be bounced via veneers in the
+ module's PLT. This allows modules to be allocated in the generic
+ vmalloc area after the dedicated module memory area has been
+ exhausted.
+
+ When running with address space randomization (KASLR), the module
+ region itself may be too far away for ordinary relative jumps and
+ calls, and so in that case, module PLTs are required and cannot be
+ disabled.
+
+ Specific errata workaround(s) might also force module PLTs to be
+ enabled (ARM64_ERRATUM_843419).
+
+ Disabling this is usually safe for small single-platform
+ configurations.
config ARM64_PSEUDO_NMI
bool "Support for NMI-like interrupts"
--
2.17.1
On Mon, Jun 17, 2019 at 03:29:59PM -0700, Florian Fainelli wrote:
> Make ARM64_MODULE_PLTS a selectable Kconfig symbol, since some people
> might have very big modules spilling out of the dedicated module area
> into vmalloc. Help text is copied from the ARM 32-bit counterpart and
> modified to a mention of KASLR and specific ARM errata workaround(s).
>
> Signed-off-by: Florian Fainelli <[email protected]>
> ---
> Changes in v3:
> - take out the part about "The modules will use slightly more memory, but after
> rounding up to page size, the actual memory footprint is usually the same.
> - take out the "If unusure say Y", since we would really prefer this to
> be off by default for maximum performance
>
> Changes in v2:
>
> - added Ard's paragraph about KASLR
> - added a paragraph about specific workarounds also requiring
> ARM64_MODULE_PLTS
>
> arch/arm64/Kconfig | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 697ea0510729..9206feaeff07 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1418,8 +1418,26 @@ config ARM64_SVE
> KVM in the same kernel image.
>
> config ARM64_MODULE_PLTS
> - bool
> + bool "Use PLTs to allow module memory to spill over into vmalloc area"
> select HAVE_MOD_ARCH_SPECIFIC
> + help
> + Allocate PLTs when loading modules so that jumps and calls whose
> + targets are too far away for their relative offsets to be encoded
> + in the instructions themselves can be bounced via veneers in the
> + module's PLT. This allows modules to be allocated in the generic
> + vmalloc area after the dedicated module memory area has been
> + exhausted.
> +
> + When running with address space randomization (KASLR), the module
> + region itself may be too far away for ordinary relative jumps and
> + calls, and so in that case, module PLTs are required and cannot be
> + disabled.
> +
> + Specific errata workaround(s) might also force module PLTs to be
> + enabled (ARM64_ERRATUM_843419).
> +
> + Disabling this is usually safe for small single-platform
> + configurations.
I think I'd still drop this last sentence, because labelling a kernel
"usually safe" without this option is a bit OTT. We'll just reject large
modules, nothing unsafe about that.
Assuming Catalin can do that when he applies, so:
Acked-by: Will Deacon <[email protected]>
Will
On Mon, Jun 17, 2019 at 03:29:59PM -0700, Florian Fainelli wrote:
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 697ea0510729..9206feaeff07 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1418,8 +1418,26 @@ config ARM64_SVE
> KVM in the same kernel image.
>
> config ARM64_MODULE_PLTS
> - bool
> + bool "Use PLTs to allow module memory to spill over into vmalloc area"
> select HAVE_MOD_ARCH_SPECIFIC
This needs a depends on MODULES now (it failed to build in one of my
tests where modules were disabled but this option was left enabled).
I'll add a patch on top.
--
Catalin
On 6/25/19 1:29 AM, Catalin Marinas wrote:
> On Mon, Jun 17, 2019 at 03:29:59PM -0700, Florian Fainelli wrote:
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 697ea0510729..9206feaeff07 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -1418,8 +1418,26 @@ config ARM64_SVE
>> KVM in the same kernel image.
>>
>> config ARM64_MODULE_PLTS
>> - bool
>> + bool "Use PLTs to allow module memory to spill over into vmalloc area"
>> select HAVE_MOD_ARCH_SPECIFIC
>
> This needs a depends on MODULES now (it failed to build in one of my
> tests where modules were disabled but this option was left enabled).
>
> I'll add a patch on top.
Ah, sorry about that, thanks, I see both in linux-next now.
--
Florian