linux-kernel - [PATCH] powerpc/32: Fix protection of kernel RAM after freeing unused memory

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Message-Id: <20170414131126.AA07A67422@localhost.localdomain>
Date:   Fri, 14 Apr 2017 15:11:26 +0200 (CEST)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/32: Fix protection of kernel RAM after freeing unused
 memory

As seen below, allthough the init sections have been freed, the
associated memory area is still marked as executable in the
page tables. This patch fixes that.

[    5.860093] Freeing unused kernel memory: 592K (c0570000 - c0604000)

---[ Start of kernel VM ]---
0xc0000000-0xc0497fff        4704K  rw  X  present dirty accessed shared
0xc0498000-0xc056ffff         864K  rw     present dirty accessed shared
0xc0570000-0xc059ffff         192K  rw  X  present dirty accessed shared
0xc05a0000-0xc7ffffff      125312K  rw     present dirty accessed shared
---[ vmalloc() Area ]---

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/mm/mem.c        |  3 +++
 arch/powerpc/mm/mmu_decl.h   |  1 +
 arch/powerpc/mm/pgtable_32.c | 20 ++++++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 9ee536ec0739..e95931c4e6cf 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -401,6 +401,9 @@ void free_initmem(void)
 {
 	ppc_md.progress = ppc_printk_progress;
 	free_initmem_default(POISON_FREE_INITMEM);
+#ifdef CONFIG_PPC32
+	remap_init_ram();
+#endif
 }
 
 #ifdef CONFIG_BLK_DEV_INITRD
diff --git a/arch/powerpc/mm/mmu_decl.h b/arch/powerpc/mm/mmu_decl.h
index f988db655e5b..d39d92600839 100644
--- a/arch/powerpc/mm/mmu_decl.h
+++ b/arch/powerpc/mm/mmu_decl.h
@@ -95,6 +95,7 @@ extern void _tlbia(void);
 
 extern void mapin_ram(void);
 extern int map_page(unsigned long va, phys_addr_t pa, int flags);
+void remap_init_ram(void);
 extern void setbat(int index, unsigned long virt, phys_addr_t phys,
 		   unsigned int size, pgprot_t prot);
 
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index a65c0b4c0669..d506bd61b629 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -323,6 +323,26 @@ get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep, pmd_t **pmdp)
         return(retval);
 }
 
+void remap_init_ram(void)
+{
+	unsigned long start = (unsigned long)_sinittext & PAGE_MASK;
+	unsigned long end = (unsigned long)_einittext;
+	unsigned long va;
+
+	for (va = start; va < end; va += PAGE_SIZE) {
+		pte_t *kpte;
+		pmd_t *kpmd;
+		pte_t pte = pfn_pte(__pa(va) >> PAGE_SHIFT, PAGE_KERNEL);
+
+		if (!get_pteptr(&init_mm, va, &kpte, &kpmd))
+			continue;
+		__set_pte_at(&init_mm, va, kpte, pte, 0);
+		wmb();
+		pte_unmap(kpte);
+	}
+	flush_tlb_kernel_range(start, end);
+}
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 
 static int __change_page_attr(struct page *page, pgprot_t prot)
-- 
2.12.0