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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=DG3BzwQ2BWylwPDcl7KrfGhx2mIF7dLUmwl61g76BeleGjxlXwR4RDqh1sN4AbaLj LCiKCPNKKZn+A3q/x0AZAtwJwqjQspJXZq6Gj4MU6eeg51aUBJC8fVM+e53znk7u7i OQoSxfM434A9LxtAKAO1Jlmfa/R0vptHUyiea5Xf3GDQSRfEJR1UQIXvaqBBKtOpcy AVto//EUOxjmaJK2YYQKuOz5qz8i2tTQuKWYati/DUVFmup3bEHu0inyoANKIPOidS StXvbk7nGpNOH4+MoZQIgOsZzrfgFScQn6oJjgAvI1D78ZdQ87LB/YAc3eQv2WkUMF EniWYTJqe8v3A== Message-ID: <30affad5-4f26-4e22-9d64-b8ece1199773@zytor.com> Date: Thu, 15 May 2025 11:11:09 -0700 Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/3] x86/xen/msr: Fix uninitialized symbol 'err' To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, jgross@suse.com, boris.ostrovsky@oracle.com, rafael@kernel.org, lenb@kernel.org References: <20250512084552.1586883-1-xin@zytor.com> <20250512084552.1586883-3-xin@zytor.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/15/2025 8:29 AM, Ingo Molnar wrote: > > * Xin Li (Intel) wrote: > >> xen_read_msr_safe() currently passes an uninitialized argument err to >> xen_do_read_msr(). But as xen_do_read_msr() may not set the argument, >> xen_read_msr_safe() could return err with an unpredictable value. >> >> To ensure correctness, initialize err to 0 (representing success) >> in xen_read_msr_safe(). >> >> Because xen_read_msr_safe() is essentially a wrapper of xen_do_read_msr(), >> the latter should be responsible for initializing the value of *err to 0. >> Thus initialize *err to 0 in xen_do_read_msr(). >> >> Fixes: 502ad6e5a619 ("x86/msr: Change the function type of native_read_msr_safe()") >> Reported-by: Dan Carpenter >> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/ >> Signed-off-by: Xin Li (Intel) >> --- >> arch/x86/xen/enlighten_pv.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c >> index 3be38350f044..01f1d441347e 100644 >> --- a/arch/x86/xen/enlighten_pv.c >> +++ b/arch/x86/xen/enlighten_pv.c >> @@ -1091,6 +1091,9 @@ static u64 xen_do_read_msr(u32 msr, int *err) >> { >> u64 val = 0; /* Avoid uninitialized value for safe variant. */ >> >> + if (err) >> + *err = 0; >> + >> if (pmu_msr_chk_emulated(msr, &val, true)) >> return val; >> >> @@ -1162,7 +1165,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err) >> >> static int xen_read_msr_safe(u32 msr, u64 *val) >> { >> - int err; >> + int err = 0; >> >> *val = xen_do_read_msr(msr, &err); >> return err; > > So why not initialize 'err' with 0 in both callers, xen_read_msr_safe() > and xen_read_msr(), and avoid all the initialization trouble in > xen_do_read_msr()? Yeah, I should make the change in xen_read_msr() too. However xen_do_read_msr() should be implemented in a defensive way to set *err properly as it's part of its return value. Actually it was so, but one of my previous cleanup patch removed it because err is no longer passed to pmu_msr_chk_emulated(). Thanks! Xin