linux-kernel - [PATCH] ARC: mm: PAE40: Cast pfn to pte_t in pfn

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Message-Id: <1480306037-15415-1-git-send-email-yuriy.kolerov@synopsys.com>
Date:   Mon, 28 Nov 2016 07:07:17 +0300
From:   Yuriy Kolerov <yuriy.kolerov@...opsys.com>
To:     linux-snps-arc@...ts.infradead.org
Cc:     Vineet.Gupta1@...opsys.com, Alexey.Brodkin@...opsys.com,
        linux-kernel@...r.kernel.org,
        Yuriy Kolerov <yuriy.kolerov@...opsys.com>
Subject: [PATCH] ARC: mm: PAE40: Cast pfn to pte_t in pfn_pte() macro

Originally pfn_pte(pfn, prot) macro had this definition:

    __pte(((pfn) << PAGE_SHIFT) | pgprot_val(prot))

The value of pfn (Page Frame Number) is shifted to the left to get the
value of pte (Page Table Entry). Usually a 4-byte value is passed to
this macro as value of pfn. However if Linux is configured with support
of PAE40 then value of pte has 8-byte type because it must contain
additional 8 bits of the physical address. Thus if value of pfn
represents a physical page frame above of 4GB boundary then
shifting of pfn to the left by PAGE_SHIFT wipes most significant
bits of the 40-bit physical address.

As a result all physical addresses above of 4GB boundary in systems
with PAE40 are mapped to virtual address incorrectly. An error may
occur when the kernel tries to unmap such bad pages:

    [ECR   ]: 0x00050100 => Invalid Read @ 0x41414144 by insn @ 0x801644c6
    [EFA   ]: 0x41414144
    [BLINK ]: unmap_page_range+0x134/0x700
    [ERET  ]: unmap_page_range+0x17a/0x700
    [STAT32]: 0x8008021e : IE K
    BTA: 0x801644c6	 SP: 0x901a5e84	 FP: 0x5ff35de8
    LPS: 0x8026462c	LPE: 0x80264630	LPC: 0x00000000
    r00: 0x8fcc4fc0	r01: 0x2fe68000	r02: 0x41414140
    r03: 0x2c05c000	r04: 0x2fe6a000	r05: 0x0009ffff
    r06: 0x901b6898	r07: 0x2fe68000	r08: 0x00000001
    r09: 0x804a807c	r10: 0x0000067e	r11: 0xffffffff
    r12: 0x80164480
    Stack Trace:
      unmap_page_range+0x17a/0x700
      unmap_vmas+0x46/0x64
      do_munmap+0x210/0x450
      SyS_munmap+0x2c/0x50
      EV_Trap+0xfc/0x100

So the value of pfn must be casted to pte_t before shifting to
ensure that 40-bit address will not be truncated:

    __pte(((pte_t) (pfn) << PAGE_SHIFT) | pgprot_val(prot))

Signed-off-by: Yuriy Kolerov <yuriy.kolerov@...opsys.com>
---
 arch/arc/include/asm/pgtable.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arc/include/asm/pgtable.h b/arch/arc/include/asm/pgtable.h
index 89eeb37..77bc51c 100644
--- a/arch/arc/include/asm/pgtable.h
+++ b/arch/arc/include/asm/pgtable.h
@@ -280,7 +280,8 @@ static inline void pmd_set(pmd_t *pmdp, pte_t *ptep)
 
 #define pte_page(pte)		pfn_to_page(pte_pfn(pte))
 #define mk_pte(page, prot)	pfn_pte(page_to_pfn(page), prot)
-#define pfn_pte(pfn, prot)	__pte(((pfn) << PAGE_SHIFT) | pgprot_val(prot))
+#define pfn_pte(pfn, prot) \
+	__pte(((pte_t) (pfn) << PAGE_SHIFT) | pgprot_val(prot))
 
 /* Don't use virt_to_pfn for macros below: could cause truncations for PAE40*/
 #define pte_pfn(pte)		(pte_val(pte) >> PAGE_SHIFT)
-- 
2.7.4