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Subject[tip:x86/urgent] x86/mm: Avoid VLA in pgd_alloc()
Commit-ID:  1be3f247c2882a82279cbcf43717581ea943b692
Gitweb: https://git.kernel.org/tip/1be3f247c2882a82279cbcf43717581ea943b692
Author: Arnd Bergmann <arnd@arndb.de>
AuthorDate: Fri, 5 Oct 2018 18:13:16 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 5 Oct 2018 18:16:55 +0200

x86/mm: Avoid VLA in pgd_alloc()

Turning on -Wvla found a new VLA usage:

arch/x86/mm/pgtable.c: In function 'pgd_alloc':
include/linux/build_bug.h:29:45: error: ISO C90 forbids variable length array 'u_pmds' [-Werror=vla]
arch/x86/mm/pgtable.c:190:34: note: in expansion of macro 'static_cpu_has'
#define PREALLOCATED_USER_PMDS (static_cpu_has(X86_FEATURE_PTI) ? \
^~~~~~~~~~~~~~
arch/x86/mm/pgtable.c:431:16: note: in expansion of macro 'PREALLOCATED_USER_PMDS'
pmd_t *u_pmds[PREALLOCATED_USER_PMDS];
^~~~~~~~~~~~~~~~~~~~~~

Use the actual size of the array that is used for X86_FEATURE_PTI
instead of the variable size.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hpe.com>
Fixes: 68664695ae57 ("Makefile: Globally enable VLA warning")
Fixes: f59dbe9ca670 ("x86/pgtable/pae: Use separate kernel PMDs for user page-table")
Link: http://lkml.kernel.org/r/20181005161333.765973-1-arnd@arndb.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/mm/pgtable.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 089e78c4effd..386b43e3e0ac 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -189,6 +189,7 @@ static void pgd_dtor(pgd_t *pgd)
*/
#define PREALLOCATED_USER_PMDS (static_cpu_has(X86_FEATURE_PTI) ? \
KERNEL_PGD_PTRS : 0)
+#define MAX_PREALLOCATED_USER_PMDS KERNEL_PGD_PTRS

void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd)
{
@@ -211,6 +212,7 @@ void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd)
/* No need to prepopulate any pagetable entries in non-PAE modes. */
#define PREALLOCATED_PMDS 0
#define PREALLOCATED_USER_PMDS 0
+#define MAX_PREALLOCATED_USER_PMDS 0
#endif /* CONFIG_X86_PAE */

static void free_pmds(struct mm_struct *mm, pmd_t *pmds[], int count)
@@ -428,8 +430,8 @@ static inline void _pgd_free(pgd_t *pgd)
pgd_t *pgd_alloc(struct mm_struct *mm)
{
pgd_t *pgd;
- pmd_t *u_pmds[PREALLOCATED_USER_PMDS];
- pmd_t *pmds[PREALLOCATED_PMDS];
+ pmd_t *u_pmds[MAX_PREALLOCATED_USER_PMDS];
+ pmd_t *pmds[MAX_PREALLOCATED_USER_PMDS];

pgd = _pgd_alloc();

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