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) <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.
Okay, I will send v1A to address this comment then.
Thanks!
Xin
Juergen
