From 184d47f0fd365108bd06ab26cdb3450b716269fd Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 8 Oct 2018 16:54:34 -0700 Subject: x86/mm: Avoid VLA in pgd_alloc() Arnd Bergmann reported that turning on -Wvla found a new (unintended) 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, which is known at build time, instead of the variable size. [ mingo: Squashed original fix with followup fix to avoid bisection breakage, wrote new changelog. ] Reported-by: Arnd Bergmann Original-written-by: Arnd Bergmann Reported-by: Borislav Petkov Signed-off-by: Kees Cook Cc: Andrew Morton Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Dave Hansen Cc: Joerg Roedel Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Toshi Kani Fixes: 1be3f247c288 ("x86/mm: Avoid VLA in pgd_alloc()") Link: http://lkml.kernel.org/r/20181008235434.GA35035@beast Signed-off-by: Ingo Molnar --- arch/x86/mm/pgtable.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 089e78c4effd..59274e2c1ac4 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -115,6 +115,8 @@ static inline void pgd_list_del(pgd_t *pgd) #define UNSHARED_PTRS_PER_PGD \ (SHARED_KERNEL_PMD ? KERNEL_PGD_BOUNDARY : PTRS_PER_PGD) +#define MAX_UNSHARED_PTRS_PER_PGD \ + max_t(size_t, KERNEL_PGD_BOUNDARY, PTRS_PER_PGD) static void pgd_set_mm(pgd_t *pgd, struct mm_struct *mm) @@ -181,6 +183,7 @@ static void pgd_dtor(pgd_t *pgd) * and initialize the kernel pmds here. */ #define PREALLOCATED_PMDS UNSHARED_PTRS_PER_PGD +#define MAX_PREALLOCATED_PMDS MAX_UNSHARED_PTRS_PER_PGD /* * We allocate separate PMDs for the kernel part of the user page-table @@ -189,6 +192,7 @@ 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) { @@ -210,7 +214,9 @@ 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 MAX_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 +434,8 @@ 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_PMDS]; pgd = _pgd_alloc(); -- cgit v1.2.3