lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 15 Jan 2021 00:54:41 +0000 From: Andrew Cooper <andrew.cooper3@...rix.com> To: Josh Poimboeuf <jpoimboe@...hat.com> CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>, Sami Tolvanen <samitolvanen@...gle.com>, Sedat Dilek <sedat.dilek@...il.com>, Kees Cook <keescook@...omium.org>, Nick Desaulniers <ndesaulniers@...gle.com>, <clang-built-linux@...glegroups.com>, Miroslav Benes <mbenes@...e.cz>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz> Subject: Re: [PATCH 17/21] x86/acpi: Convert indirect jump to retpoline 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" <rjw@...ysocki.net> >>> Cc: Len Brown <len.brown@...el.com> >>> Cc: Pavel Machek <pavel@....cz> >>> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.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 <pavel@...e.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
Powered by blists - more mailing lists