linux-hardening - [PATCH][next] x86/mm/pgtable: Fix Wstringop-overflow warnings

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Date:   Thu, 31 Mar 2022 19:58:34 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] x86/mm/pgtable: Fix Wstringop-overflow warnings

Fix the following -Wstringop-overflow warnings when building with GCC-11:

.arch/x86/mm/pgtable.c: In function ‘pgd_alloc’:
arch/x86/mm/pgtable.c:437:13: warning: ‘preallocate_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
  437 |         if (preallocate_pmds(mm, pmds, PREALLOCATED_PMDS) != 0)
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:437:13: note: referencing argument 2 of type ‘pmd_t **’
arch/x86/mm/pgtable.c:225:12: note: in a call to function ‘preallocate_pmds.constprop’
  225 | static int preallocate_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
      |            ^~~~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:440:13: warning: ‘preallocate_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
  440 |         if (preallocate_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS) != 0)
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:440:13: note: referencing argument 2 of type ‘pmd_t **’
arch/x86/mm/pgtable.c:225:12: note: in a call to function ‘preallocate_pmds.constprop’
  225 | static int preallocate_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
      |            ^~~~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:462:9: warning: ‘free_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
  462 |         free_pmds(mm, u_pmds, PREALLOCATED_USER_PMDS);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:462:9: note: referencing argument 2 of type ‘pmd_t **’
arch/x86/mm/pgtable.c:213:13: note: in a call to function ‘free_pmds.constprop’
  213 | static void free_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
      |             ^~~~~~~~~
arch/x86/mm/pgtable.c:455:9: warning: ‘pgd_prepopulate_user_pmd’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
  455 |         pgd_prepopulate_user_pmd(mm, pgd, u_pmds);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:455:9: note: referencing argument 3 of type ‘pmd_t **’
arch/x86/mm/pgtable.c:320:13: note: in a call to function ‘pgd_prepopulate_user_pmd’
  320 | static void pgd_prepopulate_user_pmd(struct mm_struct *mm,
      |             ^~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:464:9: warning: ‘free_pmds.constprop’ accessing 8 bytes in a region of size 0 [-Wstringop-overflow=]
  464 |         free_pmds(mm, pmds, PREALLOCATED_PMDS);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:464:9: note: referencing argument 2 of type ‘pmd_t **’
arch/x86/mm/pgtable.c:213:13: note: in a call to function ‘free_pmds.constprop’
  213 | static void free_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
      |             ^~~~~~~~~

by using pointer notation instead of array notation as a workaround for
the above GCC warnings.

This helps with the ongoing efforts to globally enable
-Wstringop-overflow.

Link: https://github.com/KSPP/linux/issues/181
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 arch/x86/mm/pgtable.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 3481b35cb4ec..aecaebf3c3d0 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -210,7 +210,7 @@ void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd)
 #define MAX_PREALLOCATED_USER_PMDS 0
 #endif	/* CONFIG_X86_PAE */
 
-static void free_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
+static void free_pmds(struct mm_struct *mm, pmd_t **pmds, int count)
 {
 	int i;
 
@@ -222,7 +222,7 @@ static void free_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
 		}
 }
 
-static int preallocate_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
+static int preallocate_pmds(struct mm_struct *mm, pmd_t **pmds, int count)
 {
 	int i;
 	bool failed = false;
@@ -318,7 +318,7 @@ static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t *pmds[])
 
 #ifdef CONFIG_PAGE_TABLE_ISOLATION
 static void pgd_prepopulate_user_pmd(struct mm_struct *mm,
-				     pgd_t *k_pgd, pmd_t *pmds[])
+				     pgd_t *k_pgd, pmd_t **pmds)
 {
 	pgd_t *s_pgd = kernel_to_user_pgdp(swapper_pg_dir);
 	pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
-- 
2.27.0