On 15.05.25 20:11, Xin Li wrote:
On 5/15/2025 8:29 AM, Ingo Molnar wrote:* Xin Li (Intel) <x...@zytor.com> 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 <dan.carpen...@linaro.org> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/ Signed-off-by: Xin Li (Intel) <x...@zytor.com> --- 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. Juergen
OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key
OpenPGP_signature.asc
Description: OpenPGP digital signature
