linux-kernel - [PATCH] ARC: mm: allow mprotect to make stack mappings executable

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Date:   Thu, 12 Jul 2018 15:16:34 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     <linux-snps-arc@...ts.infradead.org>
CC:     <linux-kernel@...r.kernel.org>,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>,
        <stable@...r.kernel.org>
Subject: [PATCH] ARC: mm: allow mprotect to make stack mappings executable

mprotect(EXEC) was failing for stack mappings as default vm flags was
missing MAYEXEC.

This was triggered by glibc test suite nptl/tst-execstack testcase

What is surprising is that despite running LTP for years on, we didn't
catch this issue as it lacks a directed test case.

gcc dejagnu tests with nested functions also requiring exec stack work
fine though because they rely on the GNU_STACK segment spit out by
compiler and handled in kernel elf loader.

This glibc case is different as the stack is non exec to begin with and
a dlopen of shared lib with GNU_STACK segment triggers the exec stack
proceedings using a mprotect(PROT_EXEC) which was broken.

CC: stable@...r.kernel.org
Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
 arch/arc/include/asm/page.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/include/asm/page.h b/arch/arc/include/asm/page.h
index 109baa06831c..09ddddf71cc5 100644
--- a/arch/arc/include/asm/page.h
+++ b/arch/arc/include/asm/page.h
@@ -105,7 +105,7 @@ typedef pte_t * pgtable_t;
 #define virt_addr_valid(kaddr)  pfn_valid(virt_to_pfn(kaddr))

 /* Default Permissions for stack/heaps pages (Non Executable) */
-#define VM_DATA_DEFAULT_FLAGS   (VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE)
+#define VM_DATA_DEFAULT_FLAGS   (VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)

 #define WANT_PAGE_VIRTUAL   1

-- 
2.7.4