| Message ID | 20250512084552.1586883-3-xin@zytor.com |
|---|---|
| State | New |
| Headers | show |
| Series | MSR fixes and cleanups after last round of MSR cleanups | expand |
* Xin Li (Intel) <xin@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.carpenter@linaro.org> > Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/ > Signed-off-by: Xin Li (Intel) <xin@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()? Thanks, Ingo
On 5/15/2025 8:29 AM, Ingo Molnar wrote: > > * Xin Li (Intel) <xin@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.carpenter@linaro.org> >> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/ >> Signed-off-by: Xin Li (Intel) <xin@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(). Thanks! Xin
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;
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.carpenter@linaro.org> Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/ Signed-off-by: Xin Li (Intel) <xin@zytor.com> --- arch/x86/xen/enlighten_pv.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)