Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [patch 00/38] x86/retbleed: Call depth tracking mitigation | Date | Tue, 19 Jul 2022 00:22:26 +0200 |
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On Mon, Jul 18 2022 at 23:18, Peter Zijlstra wrote: > On Mon, Jul 18, 2022 at 10:44:14PM +0200, Thomas Gleixner wrote: >> And we need input from the Clang folks because their CFI work also puts >> stuff in front of the function entry, which nicely collides. > > Right, I need to go look at the latest kCFI patches, that sorta got > side-tracked for working on all the retbleed muck :/ > > Basically kCFI wants to preface every (indirect callable) function with: > > __cfi_\func: > int3 > movl $0x12345678, %rax > int3 > int3 > \func: > endbr > \func_direct: > > Ofc, we can still put the whole: > > sarq $5, PER_CPU_VAR(__x86_call_depth); > jmp \func_direct > > thing in front of that. But it does somewhat destroy the version I had > that only needs the 10 bytes padding for the sarq.
Right, because it needs the jump. I was just chatting with Jaoa about that over IRC.
The jump slow things down. Jaoa has ideas and will reply soonish.
Thanks,
tglx
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