On 14/01/2021 19:40, Josh Poimboeuf wrote: > It's kernel policy to not have (unannotated) indirect jumps because of > Spectre v2. This one's probably harmless, but better safe than sorry. > Convert it to a retpoline. > > Cc: "Rafael J. Wysocki" <r...@rjwysocki.net> > Cc: Len Brown <len.br...@intel.com> > Cc: Pavel Machek <pa...@ucw.cz> > Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> > --- > arch/x86/kernel/acpi/wakeup_64.S | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/acpi/wakeup_64.S > b/arch/x86/kernel/acpi/wakeup_64.S > index 5d3a0b8fd379..0b371580e620 100644 > --- a/arch/x86/kernel/acpi/wakeup_64.S > +++ b/arch/x86/kernel/acpi/wakeup_64.S > @@ -7,6 +7,7 @@ > #include <asm/msr.h> > #include <asm/asm-offsets.h> > #include <asm/frame.h> > +#include <asm/nospec-branch.h> > > # Copyright 2003 Pavel Machek <pa...@suse.cz > > @@ -39,7 +40,7 @@ SYM_FUNC_START(wakeup_long64) > movq saved_rbp, %rbp > > movq saved_rip, %rax > - jmp *%rax > + JMP_NOSPEC rax > SYM_FUNC_END(wakeup_long64)
I suspect this won't work as you intend. wakeup_long64() still executes on the low mappings, not the high mappings, so the `jmp __x86_indirect_thunk_rax` under this JMP_NOSPEC will wander off into the weeds. This is why none of the startup "jmps from weird contexts onto the high mappings" have been retpolined-up. ~Andrew
