ARM: fix a cockup in 48be69a02 (ARM: move signal handlers into a vdso-like page)

Unfortunately, I never committed the fix to a nasty oops which can
occur as a result of that commit:

------------[ cut here ]------------
kernel BUG at /home/olof/work/batch/include/linux/mm.h:414!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 0 PID: 490 Comm: killall5 Not tainted 3.11.0-rc3-00288-gabe0308 #53
task: e90acac0 ti: e9be8000 task.ti: e9be8000
PC is at special_mapping_fault+0xa4/0xc4
LR is at __do_fault+0x68/0x48c

This doesn't show up unless you do quite a bit of testing; a simple
boot test does not do this, so all my nightly tests were passing fine.

The reason for this is that install_special_mapping() expects the
page array to stick around, and as this was only inserting one page
which was stored on the kernel stack, that's why this was blowing up.

Reported-by: Olof Johansson <olof@lixom.net>
Tested-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 1e6c33d01c057fc95a8b6f3e14a44c7b7d6e8233..d03b5bd889c5d0c3101ea82fde6cbd6f06d76f0a 100644 (file)
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -471,17 +471,18 @@ const char *arch_vma_name(struct vm_area_struct *vma)
                 "[sigpage]" : NULL;
 }
 
+static struct page *signal_page;
 extern struct page *get_signal_page(void);
 
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
        struct mm_struct *mm = current->mm;
-       struct page *page;
        unsigned long addr;
        int ret;
 
-       page = get_signal_page();
-       if (!page)
+       if (!signal_page)
+               signal_page = get_signal_page();
+       if (!signal_page)
                return -ENOMEM;
 
        down_write(&mm->mmap_sem);
@@ -493,7 +494,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
        ret = install_special_mapping(mm, addr, PAGE_SIZE,
                VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
-               &page);
+               &signal_page);
 
        if (ret == 0)
                mm->context.sigpage = addr;

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 0f17e06d51e60e49085beeba598c4ac4e3bba272..39e7105a9b70aa9c9904e1c90aecd7d99e85d027 100644 (file)
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -614,35 +614,32 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
        return 0;
 }
 
-static struct page *signal_page;
-
 struct page *get_signal_page(void)
 {
-       if (!signal_page) {
-               unsigned long ptr;
-               unsigned offset;
-               void *addr;
+       unsigned long ptr;
+       unsigned offset;
+       struct page *page;
+       void *addr;
 
-               signal_page = alloc_pages(GFP_KERNEL, 0);
+       page = alloc_pages(GFP_KERNEL, 0);
 
-               if (!signal_page)
-                       return NULL;
+       if (!page)
+               return NULL;
 
-               addr = page_address(signal_page);
+       addr = page_address(page);
 
-               /* Give the signal return code some randomness */
-               offset = 0x200 + (get_random_int() & 0x7fc);
-               signal_return_offset = offset;
+       /* Give the signal return code some randomness */
+       offset = 0x200 + (get_random_int() & 0x7fc);
+       signal_return_offset = offset;
 
-               /*
-                * Copy signal return handlers into the vector page, and
-                * set sigreturn to be a pointer to these.
-                */
-               memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
+       /*
+        * Copy signal return handlers into the vector page, and
+        * set sigreturn to be a pointer to these.
+        */
+       memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
 
-               ptr = (unsigned long)addr + offset;
-               flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
-       }
+       ptr = (unsigned long)addr + offset;
+       flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
 
-       return signal_page;
+       return page;
 }