lguest: make check_gpte et. al return bool.

This is a bit neater: we can immediately return if a PTE/PGD/PMD entry
is invalid (which also kills the guest).  It means we don't risk using
invalid entries as we reshuffle the code.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index 7584662..f074f34 100644 (file)
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -259,26 +259,35 @@ static void release_pte(pte_t pte)
 }
 /*:*/
 
-static void check_gpte(struct lg_cpu *cpu, pte_t gpte)
+static bool check_gpte(struct lg_cpu *cpu, pte_t gpte)
 {
        if ((pte_flags(gpte) & _PAGE_PSE) ||
-           pte_pfn(gpte) >= cpu->lg->pfn_limit)
+           pte_pfn(gpte) >= cpu->lg->pfn_limit) {
                kill_guest(cpu, "bad page table entry");
+               return false;
+       }
+       return true;
 }
 
-static void check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
+static bool check_gpgd(struct lg_cpu *cpu, pgd_t gpgd)
 {
        if ((pgd_flags(gpgd) & ~CHECK_GPGD_MASK) ||
-          (pgd_pfn(gpgd) >= cpu->lg->pfn_limit))
+           (pgd_pfn(gpgd) >= cpu->lg->pfn_limit)) {
                kill_guest(cpu, "bad page directory entry");
+               return false;
+       }
+       return true;
 }
 
 #ifdef CONFIG_X86_PAE
-static void check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
+static bool check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
 {
        if ((pmd_flags(gpmd) & ~_PAGE_TABLE) ||
-          (pmd_pfn(gpmd) >= cpu->lg->pfn_limit))
+           (pmd_pfn(gpmd) >= cpu->lg->pfn_limit)) {
                kill_guest(cpu, "bad page middle directory entry");
+               return false;
+       }
+       return true;
 }
 #endif
 
@@ -336,7 +345,8 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
                        return false;
                }
                /* We check that the Guest pgd is OK. */
-               check_gpgd(cpu, gpgd);
+               if (!check_gpgd(cpu, gpgd))
+                       return false;
                /*
                 * And we copy the flags to the shadow PGD entry.  The page
                 * number in the shadow PGD is the page we just allocated.
@@ -372,7 +382,8 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
                }
 
                /* We check that the Guest pmd is OK. */
-               check_gpmd(cpu, gpmd);
+               if (!check_gpmd(cpu, gpmd))
+                       return false;
 
                /*
                 * And we copy the flags to the shadow PMD entry.  The page
@@ -421,7 +432,8 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
         * Check that the Guest PTE flags are OK, and the page number is below
         * the pfn_limit (ie. not mapping the Launcher binary).
         */
-       check_gpte(cpu, gpte);
+       if (!check_gpte(cpu, gpte))
+               return false;
 
        /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
        gpte = pte_mkyoung(gpte);
@@ -857,7 +869,8 @@ static void do_set_pte(struct lg_cpu *cpu, int idx,
                         * micro-benchmark.
                         */
                        if (pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
-                               check_gpte(cpu, gpte);
+                               if (!check_gpte(cpu, gpte))
+                                       return;
                                set_pte(spte,
                                        gpte_to_spte(cpu, gpte,
                                                pte_flags(gpte) & _PAGE_DIRTY));