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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=JmhzoS6ELcdbp9uSIzDOg8w2fMwp3grFVOk6J/F1MTs2tTo6AeD6I2ci7Vqb9Cw+r RWtA5sW9Xgj8fDLRFSVyqE3FQb4gIV6e6j21PeHZfx/Z2nIkmN8vSMOxKamYKxtpFg DgDJbWqT3tLRjHUQTNQkGKZhcujD2j0GB2RKF18ft9cKxg2Ov9d1tg7AI5T8NGz1mM HHbQtySfIgbPkFiqWkflCI50y0dtLptX75e77lME9Z3+Xw9Hot6hMqF2DXtJ/LN9ML 1TKFVv3+JrNZLKx+1inrWt6BMWMlOwox35mY5mXit+uKZozEG9hxAG7dYb9KLpBCNh Ptgae8SZzlnYQ== Message-ID: <57f29caa-c952-4ea5-9e63-d19696512235@zytor.com> Date: Sat, 17 May 2025 09:23:14 -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: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , 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, boris.ostrovsky@oracle.com, rafael@kernel.org, lenb@kernel.org References: <20250512084552.1586883-1-xin@zytor.com> <20250512084552.1586883-3-xin@zytor.com> <30affad5-4f26-4e22-9d64-b8ece1199773@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: 8bit On 5/16/2025 6:42 AM, Jürgen Groß wrote: > On 15.05.25 20:11, Xin Li wrote: >> 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(). > > xen_do_read_msr() is usable only in enlighten_pv.c as it is static. > > So I'd prefer to drop setting err to 0 in xen_do_read_msr() initially > and to set err to 0 in all callers. Okay, I will send v1A to address this comment then. Thanks! Xin > Juergen