Message ID | 20190617223000.11403-1-f.fainelli@gmail.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [v3] arm64: Allow user selection of ARM64_MODULE_PLTS | expand |
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 <f.fainelli@gmail.com> > --- > 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 <will.deacon@arm.com> 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.
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.
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"
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 <f.fainelli@gmail.com> --- 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(-)