linux-kernel - [RFC PATCH 5/6] pkeys: Up level pkey

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Date:   Fri, 10 Jun 2022 16:35:32 -0700
From:   ira.weiny@...el.com
To:     linux-api@...r.kernel.org
Cc:     Ira Weiny <ira.weiny@...el.com>, ahaas@...omium.org,
        clemensb@...omium.org, gdeepti@...omium.org,
        jkummerow@...omium.org, manoskouk@...omium.org,
        thibaudm@...omium.org, Florian Weimer <fweimer@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: [RFC PATCH 5/6] pkeys: Up level pkey_free() checks

From: Ira Weiny <ira.weiny@...el.com>

x86 is missing a hardware check for pkey support in pkey_free().  While
the net result is the same (-EINVAL returned), pkey_free() has well
defined behavior which will be easier to maintain in one place.

For powerpc the return code is -1 rather than -EINVAL.  This changes
that behavior slightly but this is very unlikely to break any user
space.

Lift the checks for pkey_free() to the core mm code and ensure
consistency with returning -EINVAL.

Cc: ahaas@...omium.org
Cc: clemensb@...omium.org
Cc: gdeepti@...omium.org
Cc: jkummerow@...omium.org
Cc: manoskouk@...omium.org
Cc: thibaudm@...omium.org
Cc: Florian Weimer <fweimer@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-api@...r.kernel.org
Cc: Sohil Mehta <sohil.mehta@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Signed-off-by: Ira Weiny <ira.weiny@...el.com>

---
Thanks to Sohil for suggesting I mention the powerpc return value in the
commit message.

Also Sohil suggested changing mm_pkey_free() from int to void.  This is
added as a separate patch with his suggested by.
---
 arch/powerpc/include/asm/pkeys.h | 6 ------
 arch/x86/include/asm/pkeys.h     | 3 ---
 mm/mprotect.c                    | 8 ++++++--
 3 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index 2c8351248793..e96aa91f817b 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -107,12 +107,6 @@ static inline int mm_pkey_alloc(struct mm_struct *mm)
 
 static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
 {
-	if (!mmu_has_feature(MMU_FTR_PKEY))
-		return -1;
-
-	if (!mm_pkey_is_allocated(mm, pkey))
-		return -EINVAL;
-
 	__mm_pkey_free(mm, pkey);
 
 	return 0;
diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h
index 2e6c04d8a45b..da02737cc4d1 100644
--- a/arch/x86/include/asm/pkeys.h
+++ b/arch/x86/include/asm/pkeys.h
@@ -107,9 +107,6 @@ int mm_pkey_alloc(struct mm_struct *mm)
 static inline
 int mm_pkey_free(struct mm_struct *mm, int pkey)
 {
-	if (!mm_pkey_is_allocated(mm, pkey))
-		return -EINVAL;
-
 	mm_set_pkey_free(mm, pkey);
 
 	return 0;
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 56d35de33725..41458e729c27 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -803,10 +803,14 @@ SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
 
 SYSCALL_DEFINE1(pkey_free, int, pkey)
 {
-	int ret;
+	int ret = -EINVAL;
+
+	if (!arch_pkeys_enabled())
+		return ret;
 
 	mmap_write_lock(current->mm);
-	ret = mm_pkey_free(current->mm, pkey);
+	if (mm_pkey_is_allocated(current->mm, pkey))
+		ret = mm_pkey_free(current->mm, pkey);
 	mmap_write_unlock(current->mm);
 
 	/*
-- 
2.35.1