On 2025-09-09 at 10:24:22 +0200, Maciej Wieczor-Retman wrote: >On 2025-09-08 at 22:19:05 +0200, Andrey Konovalov wrote: >>On Mon, Sep 8, 2025 at 3:09 PM Maciej Wieczor-Retman >><maciej.wieczor-retman@xxxxxxxxx> wrote: >>> >>> >>I recall there were some corner cases where this code path got called in outline >>> >>mode, didn't have a mismatch but still died due to the die() below. But I'll >>> >>recheck and either apply what you wrote above or get add a better explanation >>> >>to the patch message. >>> > >>> >Okay, so the int3_selftest_ip() is causing a problem in outline mode. >>> > >>> >I tried disabling kasan with kasan_disable_current() but thinking of it now it >>> >won't work because int3 handler will still be called and die() will happen. >>> >>> Sorry, I meant to write that kasan_disable_current() works together with >>> if(!kasan_report()). Because without checking kasan_report()' return >>> value, if kasan is disabled through kasan_disable_current() it will have no >>> effect in both inline mode, and if int3 is called in outline mode - the >>> kasan_inline_handler will lead to die(). >> >>So do I understand correctly, that we have no way to distinguish >>whether the int3 was inserted by the KASAN instrumentation or natively >>called (like in int3_selftest_ip())? >> >>If so, I think that we need to fix/change the compiler first so that >>we can distinguish these cases. And only then introduce >>kasan_inline_handler(). (Without kasan_inline_handler(), the outline >>instrumentation would then just work, right?) >> >>If we can distinguish them, then we should only call >>kasan_inline_handler() for the KASAN-inserted int3's. This is what we >>do on arm64 (via brk and KASAN_BRK_IMM). And then int3_selftest_ip() >>should not be affected. > >Looking at it again I suppose LLVM does pass a number along metadata to the >int3. I didn't notice because no other function checks anything in the x86 int3 >handler, compared to how it's done on arm64 with brk. > >So right, thanks, after fixing it up it shouldn't affect the int3_selftest_ip(). But as Peter Zijlstra noticed, x86 already uses the #UD instruction similarly to BRK on arm64. So I think I'll use this one here, and then change INT3 to UD in the LLVM patch. -- Kind regards Maciej Wieczór-Retman
