Hi Sayali,
Le 04/03/2026 à 06:35, Sayali Patil a écrit :
On powerpc with PREEMPT_FULL or PREEMPT_LAZY and function tracing enabled,
KUAP warnings can be triggered from the VMX usercopy path under memory
stress workloads.
KUAP requires that no subfunctions are called once userspace access has
been enabled. The existing VMX copy implementation violates this
requirement by invoking enter_vmx_usercopy() from the assembly path after
userspace access has already been enabled. If preemption occurs
in this window, the AMR state may not be preserved correctly,
leading to unexpected userspace access state and resulting in
KUAP warnings.
Fix this by restructuring the VMX usercopy flow so that VMX selection
and VMX state management are centralized in raw_copy_tofrom_user(),
which is invoked by the raw_copy_{to,from,in}_user() wrappers.
The new flow is:
- raw_copy_{to,from,in}_user() calls raw_copy_tofrom_user()
- raw_copy_tofrom_user() decides whether to use the VMX path
based on size and CPU capability
- Call enter_vmx_usercopy() before enabling userspace access
- Enable userspace access as per the copy direction
and perform the VMX copy
- Disable userspace access as per the copy direction
- Call exit_vmx_usercopy()
- Fall back to the base copy routine if the VMX copy faults
With this change, the VMX assembly routines no longer perform VMX state
management or call helper functions; they only implement the
copy operations.
The previous feature-section based VMX selection inside
__copy_tofrom_user_power7() is removed, and a dedicated
__copy_tofrom_user_power7_vmx() entry point is introduced.
This ensures correct KUAP ordering, avoids subfunction calls
while KUAP is unlocked, and eliminates the warnings while preserving
the VMX fast path.
Fixes: de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access
Protection")
Reported-by: Shrikanth Hegde <[email protected]>
Closes:
https://lore.kernel.org/all/[email protected]/
Suggested-by: Christophe Leroy <[email protected]>
Co-developed-by: Aboorva Devarajan <[email protected]>
Signed-off-by: Aboorva Devarajan <[email protected]>
Signed-off-by: Sayali Patil <[email protected]>
That looks almost good, some editorial comments below.
With those fixed, you can add Reviewed-by: Christophe Leroy (CS GROUP)
<[email protected]>
---
v2->v3
- Addressd as per review feedback by removing usercopy_mode enum
and using the copy direction directly for KUAP permission handling.
- Integrated __copy_tofrom_user_vmx() functionality into
raw_copy_tofrom_user() in uaccess.h as a static __always_inline
implementation.
- Exported enter_vmx_usercopy() and exit_vmx_usercopy()
to support VMX usercopy handling from the common path.
v2: https://lore.kernel.org/all/[email protected]/
---
arch/powerpc/include/asm/uaccess.h | 66 ++++++++++++++++++++++--------
arch/powerpc/lib/copyuser_64.S | 1 +
arch/powerpc/lib/copyuser_power7.S | 45 +++++++-------------
arch/powerpc/lib/vmx-helper.c | 2 +
4 files changed, 66 insertions(+), 48 deletions(-)
diff --git a/arch/powerpc/include/asm/uaccess.h
b/arch/powerpc/include/asm/uaccess.h
index ba1d878c3f40..8fd412671025 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -15,6 +15,9 @@
#define TASK_SIZE_MAX TASK_SIZE_USER64
#endif
+/* Threshold above which VMX copy path is used */
+#define VMX_COPY_THRESHOLD 3328
+
#include <asm-generic/access_ok.h>
/*
@@ -326,40 +329,67 @@ do {
\
extern unsigned long __copy_tofrom_user(void __user *to,
const void __user *from, unsigned long size);
-#ifdef __powerpc64__
-static inline unsigned long
-raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
+unsigned long __copy_tofrom_user_base(void __user *to,
+ const void __user *from, unsigned long size);
+
+unsigned long __copy_tofrom_user_power7_vmx(void __user *to,
+ const void __user *from, unsigned long size);
+
+
Remove one line.
+static __always_inline bool will_use_vmx(unsigned long n)
+{
+ return IS_ENABLED(CONFIG_ALTIVEC) &&
+ cpu_has_feature(CPU_FTR_VMX_COPY) &&
+ n > VMX_COPY_THRESHOLD;
Avoid too many line when possible. Nowadays up to 100 chars per line are
allowed.
Take care of alignment of second line, the second line should start at
same position as IS_ENABLED, meaning you have to insert 7 spaces instead
of a tab.
+}
+
+static __always_inline unsigned long raw_copy_tofrom_user(void __user *to,
+ const void __user *from, unsigned long n,
+ unsigned long dir)
Subsequent lines should start at same position as the ( of the first
line, therefore I'd suggest following form instead:
static __always_inline unsigned long
raw_copy_tofrom_user(void __user *to,const void __user *from, unsigned
long n, unsigned long dir)
{
unsigned long ret;
- barrier_nospec();
- allow_user_access(to, KUAP_READ_WRITE);
+ if (will_use_vmx(n) && enter_vmx_usercopy()) {
+ allow_user_access(to, dir);
+ ret = __copy_tofrom_user_power7_vmx(to, from, n);
+ prevent_user_access(dir);
+ exit_vmx_usercopy();
+
+ if (unlikely(ret)) {
+ allow_user_access(to, dir);
+ ret = __copy_tofrom_user_base(to, from, n);
+ prevent_user_access(dir);
+ }
+ return ret;
+ }
+
+ allow_user_access(to, dir);
ret = __copy_tofrom_user(to, from, n);
- prevent_user_access(KUAP_READ_WRITE);
+ prevent_user_access(dir);
return ret;
}
+
+#ifdef __powerpc64__
I know it was already there before, but checkpatch is not happy about
__power64__. It should be replaced by CONFIG_PPC64.
+static inline unsigned long
+raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
+{
+ barrier_nospec();
+ return raw_copy_tofrom_user(to, from, n, KUAP_READ_WRITE);
+}
#endif /* __powerpc64__ */
static inline unsigned long raw_copy_from_user(void *to,
const void __user *from, unsigned long n)
Same problem with alignment of second line. Prefer the form used for
raw_copy_in_user() or raw_copy_to_user(), ie:
static inline unsigned long
raw_copy_from_user(void *to, const void __user *from, unsigned long n)
{
- unsigned long ret;
-
- allow_user_access(NULL, KUAP_READ);
- ret = __copy_tofrom_user((__force void __user *)to, from, n);
- prevent_user_access(KUAP_READ);
- return ret;
+ return raw_copy_tofrom_user((__force void __user *)to, from,
+ n, KUAP_READ);
100 chars are allowed per line, this should fit on a single line.
}
static inline unsigned long
raw_copy_to_user(void __user *to, const void *from, unsigned long n)
{
- unsigned long ret;
-
- allow_user_access(to, KUAP_WRITE);
- ret = __copy_tofrom_user(to, (__force const void __user *)from, n);
- prevent_user_access(KUAP_WRITE);
- return ret;
+ return raw_copy_tofrom_user(to, (__force const void __user *)from,
+ n, KUAP_WRITE);
100 chars are allowed per line, this should fit on a single line.
}
unsigned long __arch_clear_user(void __user *addr, unsigned long size);
Run checkpatch before submitting patches:
$ ./scripts/checkpatch.pl --strict -g HEAD~
CHECK: Alignment should match open parenthesis
#83: FILE: arch/powerpc/include/asm/uaccess.h:333:
+unsigned long __copy_tofrom_user_base(void __user *to,
+ const void __user *from, unsigned long size);
CHECK: Alignment should match open parenthesis
#86: FILE: arch/powerpc/include/asm/uaccess.h:336:
+unsigned long __copy_tofrom_user_power7_vmx(void __user *to,
+ const void __user *from, unsigned long size);
CHECK: Please don't use multiple blank lines
#88: FILE: arch/powerpc/include/asm/uaccess.h:338:
+
+
CHECK: Alignment should match open parenthesis
#97: FILE: arch/powerpc/include/asm/uaccess.h:347:
+static __always_inline unsigned long raw_copy_tofrom_user(void __user *to,
+ const void __user *from, unsigned long n,
CHECK: architecture specific defines should be avoided
#125: FILE: arch/powerpc/include/asm/uaccess.h:372:
+#ifdef __powerpc64__
total: 0 errors, 0 warnings, 5 checks, 212 lines checked
NOTE: For some of the reported defects, checkpatch may be able to
mechanically convert to the typical style using --fix or
--fix-inplace.
Commit 3a44f6614d88 ("powerpc: fix KUAP warning in VMX usercopy path")
has style problems, please review.
NOTE: If any of the errors are false positives, please report
them to the maintainer, see CHECKPATCH in MAINTAINERS.
