On 14/01/2021 23:47, Josh Poimboeuf wrote: > 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" <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. > D'oh. Of course it wouldn't be that easy. I suppose the other two > retpoline patches (15 and 21) are bogus as well.
If by 21 you mean 19, then most likely, yes. They're all low=>high jumps in weird contexts. ~Andrew
