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keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <20260819180735.135911-1-andrewprecious388@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-purgate-ID: tlsNG-42698a/1787215530-AB6D29EA-36A04AE0/0/0 X-purgate-type: clean X-purgate-size: 2605 On 19.08.2026 20:07, Andrew Mbugua wrote: > While running the x86_instruction_emulator fuzzer via AFL, I encountered an assertion failure in the emul_test_read_xcr() function. Thanks for the report. > The fuzzer is able to generate a CPU state where cpu_has_xsave is false. I'm having trouble here: cpu_policy isn't populated from fuzzing input, and /* Intentionally checking OSXSAVE here. */ #define cpu_has_xsave (cpu_policy.basic.raw[1].c & (1u << 27)) would mean that upon filling cpu_policy (emul_test_init() -> x86_cpu_policy_fill_native()) the OSXSAVE bit would be clear. Are you suggesting you did the fuzzing on some really old hardware? > If the fuzzer then generates & feeds an instruction containing AVX,the emulator > attempts to fetch the FPU state via x86emul_get_fpu(), which then calls emul_test_read_xcr() and hits the ASSERT(cpu_has_xsave). This assertion crashes the fuzzer. > > The crash: > 1. $ ./afl-harness < findings_dir/master01/... > afl-harness: ../../tests/x86_emulator/x86-emulate.c:179: emul_test_read_xcr: Assertion `cpu_has_xsave' failed. > Aborted > > 2. The stacktrace: > (gdb) bt > data_p=data_p@entry=0x55555604f320 "\244\264\336\346\337\001\254%\247R\216d\204*\234\377\377\224λ\3237/\365ʿX\266?\353\036\227/\0323\351dj\257\v\207\031V֖\235{\036\225|:M\330\336 \314V:&\357\306@\224\331,\301\300\372FW\262.\020\\\276\244\203\242\276\262\022!\337)F&\261\2064\200\200\377I;J\376X41\2061\206\325 \021\017F\026\267\275\340\361\357)\255\343\237n\377\374n\357#ֽ\226\365d", > size=size@entry=580) at fuzz-emul.c:934 This can't be the complete stack trace. > Possible fixes: > To prevent the fuzzer from getting stuck on this state,would it be better for emul_test_read_xcr to return X86EMUL_UNHANDLEABLE (or something similar) instead of ASSERT(cpu_has_xsave) ? No, I think the assertion is legitimate there. After sending this reply, I'll post two patches taken off of the (unposted) APX series I have pending, which I think get things into better shape (and which, with the minor editing I had to do to pull them out of that series, should be fine to move ahead). On top of that we then will want to add some sanitization of input state in the fuzzing harness: CR4.OSXSAVE set and CPUID.XSAVE clear are clearly contradictory. There are other impossible combinations, and I think we may want to address some of them at the same time, and we already have sanitize_input() there. Please let us know whether you'd be willing / interested to make changes there, or whether we (perhaps I) should. Jan