On Thu, Jan 14, 2021 at 10:59:39PM +0000, Andrew Cooper wrote: > 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" <[email protected]> > > Cc: Len Brown <[email protected]> > > Cc: Pavel Machek <[email protected]> > > Signed-off-by: Josh Poimboeuf <[email protected]> > > --- > > 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 <[email protected] > > > > @@ -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.
D'oh. Of course it wouldn't be that easy. I suppose the other two retpoline patches (15 and 21) are bogus as well. -- Josh
