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Thu, 09 Apr 2026 02:21:09 -0700 (PDT) Message-ID: <2fa2fb41-cb62-4a1b-84cf-822b2f97bc2b@suse.com> Date: Thu, 9 Apr 2026 11:21:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Teddy Astie , Stewart Hildebrand From: Jan Beulich Subject: [PATCH] x86/APIC: handle overflow in TMICT calculation Autocrypt: addr=jbeulich@suse.com; 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 Content-Transfer-Encoding: quoted-printable X-purgate-ID: tlsNG-c1860d/1775726470-7694D497-3B324977/0/0 X-purgate-type: clean X-purgate-size: 1595 X-ZohoMail-DKIM: pass (identity @suse.com) X-ZM-MESSAGEID: 1775726488404158500 Content-Type: text/plain; charset="utf-8" With an expiry value on the order of 20 hours, and with a bus scale value of 256k (as supplied by qemu), the (signed) multiplication will be UB. As we've checked that the value is positive, we mean unsigned multiplication anyway. Yet let's play safe against even larger expiry and bus scale values, leveraging the compiler builtin that there is for this purpose. While there also drop the stray cast from the actual TMICT write. Fixes: 9062553a0dc1 ("added time and accurate timer support") Fixes: b95beb185810 ("x86: Clean up APIC local timer handling") Reported-by: Stewart Hildebrand Signed-off-by: Jan Beulich Acked-by: Andrew Cooper Tested-by: Stewart Hildebrand --- Sadly neither gcc5 nor gcc15 properly optimize the (effectively) two uses of the 0xffffffffU constant: Both use a 2nd register to load the constant (really 0xfffffffeU unless <=3D is used) a 2nd time. --- a/xen/arch/x86/apic.c +++ b/xen/arch/x86/apic.c @@ -1224,10 +1224,16 @@ int reprogram_timer(s_time_t timeout) } =20 if ( timeout && ((expire =3D timeout - NOW()) > 0) ) - apic_tmict =3D min_t(uint64_t, (bus_scale * expire) >> BUS_SCALE_S= HIFT, - UINT32_MAX); + { + unsigned long product; =20 - apic_write(APIC_TMICT, (unsigned long)apic_tmict); + apic_tmict =3D UINT32_MAX; + if ( !__builtin_umull_overflow(bus_scale, expire, &product) && + (product >>=3D BUS_SCALE_SHIFT) < apic_tmict ) + apic_tmict =3D product; + } + + apic_write(APIC_TMICT, apic_tmict); =20 return apic_tmict || !timeout; }