[PATCH, REGRESSION v4] mm: make apply_to_page_range more robust

[PATCH, REGRESSION v4] mm: make apply_to_page_range more robust

[Mika Penttilä]

Recent changes (4.4.0+) in module loader triggered oops on ARM : 

The module in question is in-tree module :
drivers/misc/ti-st/st_drv.ko

The BUG is here :

[ 53.638335] ------------[ cut here ]------------
[ 53.642967] kernel BUG at mm/memory.c:1878!
[ 53.647153] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
[ 53.652987] Modules linked in:
[ 53.656061] CPU: 0 PID: 483 Comm: insmod Not tainted 4.4.0 #3
[ 53.661808] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[ 53.668338] task: a989d400 ti: 9e6a2000 task.ti: 9e6a2000
[ 53.673751] PC is at apply_to_page_range+0x204/0x224
[ 53.678723] LR is at change_memory_common+0x90/0xdc
[ 53.683604] pc : [<800ca0ec>] lr : [<8001d668>] psr: 600b0013
[ 53.683604] sp : 9e6a3e38 ip : 8001d6b4 fp : 7f0042fc
[ 53.695082] r10: 00000000 r9 : 9e6a3e90 r8 : 00000080
[ 53.700309] r7 : 00000000 r6 : 7f008000 r5 : 7f008000 r4 : 7f008000
[ 53.706837] r3 : 8001d5a4 r2 : 7f008000 r1 : 7f008000 r0 : 80b8d3c0
[ 53.713368] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
[ 53.720504] Control: 10c5387d Table: 2e6b804a DAC: 00000055
[ 53.726252] Process insmod (pid: 483, stack limit = 0x9e6a2210)
[ 53.732173] Stack: (0x9e6a3e38 to 0x9e6a4000)
[ 53.736532] 3e20: 7f007fff 7f008000
[ 53.744714] 3e40: 80b8d3c0 80b8d3c0 00000000 7f007000 7f00426c 7f008000 00000000 7f008000
[ 53.752895] 3e60: 7f004140 7f008000 00000000 00000080 00000000 00000000 7f0042fc 8001d668
[ 53.761076] 3e80: 9e6a3e90 00000000 8001d6b4 7f00426c 00000080 00000000 9e6a3f58 7f004140
[ 53.769257] 3ea0: 7f004240 7f00414c 00000000 8008bbe0 00000000 7f000000 00000000 00000000
[ 53.777438] 3ec0: a8b12f00 0001cfd4 7f004250 7f004240 80b8159c 00000000 000000e0 7f0042fc
[ 53.785619] 3ee0: c183d000 000074f8 000018fd 00000000 0b30000c 00000000 00000000 7f002024
[ 53.793800] 3f00: 00000002 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 53.801980] 3f20: 00000000 00000000 00000000 00000000 00000040 00000000 00000003 0001cfd4
[ 53.810161] 3f40: 0000017b 8000f7e4 9e6a2000 00000000 00000002 8008c498 c183d000 000074f8
[ 53.818342] 3f60: c1841588 c1841409 c1842950 00005000 000052a0 00000000 00000000 00000000
[ 53.826523] 3f80: 00000023 00000024 0000001a 0000001e 00000016 00000000 00000000 00000000
[ 53.834703] 3fa0: 003e3d60 8000f640 00000000 00000000 00000003 0001cfd4 00000000 003e3d60
[ 53.842884] 3fc0: 00000000 00000000 003e3d60 0000017b 003e3d20 7eabc9d4 76f2c000 00000002
[ 53.851065] 3fe0: 7eabc990 7eabc980 00016320 76e81d00 600b0010 00000003 00000000 00000000
[ 53.859256] [<800ca0ec>] (apply_to_page_range) from [<8001d668>] (change_memory_common+0x90/0xdc)
[ 53.868139] [<8001d668>] (change_memory_common) from [<8008bbe0>] (load_module+0x194c/0x2068)
[ 53.876671] [<8008bbe0>] (load_module) from [<8008c498>] (SyS_finit_module+0x64/0x74)
[ 53.884512] [<8008c498>] (SyS_finit_module) from [<8000f640>] (ret_fast_syscall+0x0/0x34)
[ 53.892694] Code: e0834104 eaffffbc e51a1008 eaffffac (e7f001f2)
[ 53.898792] ---[ end trace fe43fc78ebde29a3 ]---

    
apply_to_page_range gets zero length resulting in triggering :
   
  BUG_ON(addr >= end)

This is regression and a consequence of changes in module section handling.

BUG_ON() is not needed here and would need all call sites to be checked
because there may be callers that expect zero size to succeed and BUG_ON allows
easy way to DOS.

With this patch loading this module throws out a warning but that can be
handled in arch code with a separate patch.

v2: add more explanation
v3: added even more explanation and stack trace, tagged as regression
v4: change BUG_ON() to WARN_ON() and return -EINVAL

Signed-off-by: Mika PenttilA? mika.penttila@nextfour.com
---

diff --git a/mm/memory.c b/mm/memory.c
index 30991f8..9178ee6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1871,7 +1871,9 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
        unsigned long end = addr + size;
        int err;
 
-       BUG_ON(addr >= end);
+       if (WARN_ON(addr >= end))
+               return -EINVAL;
+
        pgd = pgd_offset(mm, addr);
        do {
                next = pgd_addr_end(addr, end);


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Re: [PATCH, REGRESSION v4] mm: make apply_to_page_range more robust

[David Rientjes]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 753 bytes --]

On Fri, 22 Jan 2016, Mika PenttilA? wrote:

> diff --git a/mm/memory.c b/mm/memory.c
> index 30991f8..9178ee6 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1871,7 +1871,9 @@ int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
>         unsigned long end = addr + size;
>         int err;
>  
> -       BUG_ON(addr >= end);
> +       if (WARN_ON(addr >= end))
> +               return -EINVAL;
> +
>         pgd = pgd_offset(mm, addr);
>         do {
>                 next = pgd_addr_end(addr, end);

This would be fine as a second patch in a 2-patch series.  The first patch 
should fix change_memory_common() for numpages == 0 by returning without 
ever calling this function and triggering the WARN_ON().  Let's fix the 
problem.