linux-kernel - [PATCH v3] arch : arm : add a criteria for pfn

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Message-Id: <1566193808-9153-1-git-send-email-huangzhaoyang@gmail.com>
Date:   Mon, 19 Aug 2019 13:50:08 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Russell King <linux@...linux.org.uk>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Rob Herring <robh@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Doug Berger <opendmb@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] arch : arm : add a criteria for pfn_valid

From: Zhaoyang Huang <zhaoyang.huang@...soc.com>

pfn_valid can be wrong when parsing a invalid pfn whose phys address
exceeds BITS_PER_LONG as the MSB will be trimed when shifted.

The issue originally arise from bellowing call stack, which corresponding to
an access of the /proc/kpageflags from userspace with a invalid pfn parameter
and leads to kernel panic.

[46886.723249] c7 [<c031ff98>] (stable_page_flags) from [<c03203f8>]
[46886.723264] c7 [<c0320368>] (kpageflags_read) from [<c0312030>]
[46886.723280] c7 [<c0311fb0>] (proc_reg_read) from [<c02a6e6c>]
[46886.723290] c7 [<c02a6e24>] (__vfs_read) from [<c02a7018>]
[46886.723301] c7 [<c02a6f74>] (vfs_read) from [<c02a778c>]
[46886.723315] c7 [<c02a770c>] (SyS_pread64) from [<c0108620>]
(ret_fast_syscall+0x0/0x28)

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
---
v2: use __pfn_to_phys/__phys_to_pfn instead of max_pfn as the criteria
v3: update commit message to describe the defection's context
---
 arch/arm/mm/init.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index c2daabb..cc769fa 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -177,6 +177,11 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
 #ifdef CONFIG_HAVE_ARCH_PFN_VALID
 int pfn_valid(unsigned long pfn)
 {
+	phys_addr_t addr = __pfn_to_phys(pfn);
+
+	if (__phys_to_pfn(addr) != pfn)
+		return 0;
+
 	return memblock_is_map_memory(__pfn_to_phys(pfn));
 }
 EXPORT_SYMBOL(pfn_valid);
-- 
1.9.1