On Tue, Sep 08, 2009 at 05:06:32PM +0400, Maxim Uvarov wrote:
> Patch is attached.
Please send patches inline.
> TLB exception handler incorrecly handles situation
> with wrong vmalloc'ed addresses. This patch adds
> verifications for vmalloc'ed addresses (similar to
> x86_64 implementation). So the code now traps inside
> do_page_fault() on access to the wrong area.
>
> Signed-off-by: Maxim Uvarov <muvarov@xxxxxxxxxxxxx>
>
> Test case:
>
> #include <linux/module.h>
> #include <linux/init.h>
> #include <linux/kernel.h>
> #include <linux/kthread.h>
> #include <linux/delay.h>
>
> static struct task_struct *ts;
> static int example_thread(void *dummy)
> {
> void *ptr;
> ptr = vmalloc(16*1024*1024);
> for(;;)
> {
> msleep(100);
> }
> }
So your test case allocates vmalloc memory but never touches it.
>
> static void run_vmalloc(void *unused)
> {
> ts=kthread_run(example_thread,NULL,"vtest");
> }
> int init_module (void)
> {
> run_vmalloc(NULL);
> return 0;
> }
>
> void cleanup_module (void)
> { /*Nothing*/}
>
>
> Originally kernel trapped on BUG() inside exit_mmap() and it was impossible
> to see what has happened. After this patch applied, nice back trace will be
> generated:
>
> CPU 0 Unable to handle kernel paging request at virtual address c00000000036a148
> Oops[#1]:
> Cpu 0
> $ 0 : 0000000000000000 ffffffff81940000 0000000000000000 00000000ffff05a7
> $ 4 : 0000000000000000 ffffffffffffffff ffffffff81a0b7d0 ffffffff811983e4
> $ 8 : ffffffff817407b0 0000000000000000 0000000000000000 0000000000000000
> $12 : a80000003374bfe0 0000000000008c00 ffffffff811e9df8 0000000000000000
> $16 : ffffffff81164a68 a8000000352a3c50 c00000000036a0e8 0000000000000000
> $20 : 0000000000000000 0000000000000000 0000000000000000 0000000000000000
> $24 : 0000000000000002 a8000000337bb1a0
> $28 : a800000033748000 a80000003374bf70 a80000003374bf70 c00000000036a148
> Hi : 0000000000000000
> Lo : 000000000000a311
> epc : c00000000036a148 0xc00000000036a148 Tainted: P
> ra : c00000000036a148 0xc00000000036a148 <-- dead in kernel module vtest
> Status: 10008ce3 KX SX UX KERNEL EXL IE
> Cause : 00000008
> BadVA : c00000000036a148
> PrId : 000d0408
> Modules linked in:
> Process vtest (pid: 723, threadinfo=a800000033748000, task=a800000034530340)
> Stack : 0000000000000000 a80000003374bf90 ffffffff81176530 ffffffff81176488
> ffffffffffffffff ffffffffffffffff 0000000000000000 0000000000000000
> 0000000000000000 a80000003374bfd0 ffffffff81125024 0000000000000000
> 0000000000000000 0000000000000000 5a5a5a5a5a5a5a5a 5a5a5a5a5a5a5a5a
> 5a5a5a5a5a5a5a5a 5a5a5a5a5a5a5aa5
> Call Trace:
> [<ffffffff81176530>] kthread+0x198/0x1f0
> [<ffffffff81176488>] kthread+0xf0/0x1f0
> [<ffffffff81125024>] kernel_thread_helper+0x14/0x20
>
>
> Code: (Bad address in epc)
This is a 64-bit kernel crash ...
> Index: linux-2.6.21/arch/mips/mm/fault.c
> ===================================================================
> --- linux-2.6.21.orig/arch/mips/mm/fault.c
> +++ linux-2.6.21/arch/mips/mm/fault.c
> @@ -282,22 +282,32 @@ vmalloc_fault:
> pte_t *pte_k;
>
> pgd = (pgd_t *) pgd_current[raw_smp_processor_id()] + offset;
> - pgd_k = init_mm.pgd + offset;
> + pgd_k = pgd_offset_k(address);
>
> if (!pgd_present(*pgd_k))
> goto no_context;
> - set_pgd(pgd, *pgd_k);
> + if (unlikely(!pgd_present(*pgd)))
> + set_pgd(pgd, *pgd_k);
> + else if (pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_k))
> + goto no_context;
>
> pud = pud_offset(pgd, address);
> pud_k = pud_offset(pgd_k, address);
> if (!pud_present(*pud_k))
> goto no_context;
> + if (pud_none(*pud) ||
> + pud_page_vaddr(*pud) != pud_page_vaddr(*pud_k))
> + goto no_context;
>
> pmd = pmd_offset(pud, address);
> pmd_k = pmd_offset(pud_k, address);
> if (!pmd_present(*pmd_k))
> goto no_context;
> - set_pmd(pmd, *pmd_k);
> + if (!pmd_present(*pmd))
> + set_pmd(pmd, *pmd_k);
> + else
> + if (pmd_page(*pmd) != pmd_page(*pmd_k))
> + goto no_context;
>
> pte_k = pte_offset_kernel(pmd_k, address);
> if (!pte_present(*pte_k))
... but on 64-bit kernels vmalloc_fault: should not be reached ever.
Ralf
