[PATCH] powerpc/fadump: handle crash memory ranges array overflow
Hari Bathini
hbathini at linux.vnet.ibm.com
Mon Aug 6 15:35:02 AEST 2018
On Monday 06 August 2018 09:52 AM, Mahesh Jagannath Salgaonkar wrote:
> On 07/31/2018 07:26 PM, Hari Bathini wrote:
>> Crash memory ranges is an array of memory ranges of the crashing kernel
>> to be exported as a dump via /proc/vmcore file. The size of the array
>> is set based on INIT_MEMBLOCK_REGIONS, which works alright in most cases
>> where memblock memory regions count is less than INIT_MEMBLOCK_REGIONS
>> value. But this count can grow beyond INIT_MEMBLOCK_REGIONS value since
>> commit 142b45a72e22 ("memblock: Add array resizing support").
>>
>> On large memory systems with a few DLPAR operations, the memblock memory
>> regions count could be larger than INIT_MEMBLOCK_REGIONS value. On such
>> systems, registering fadump results in crash or other system failures
>> like below:
>>
>> task: c00007f39a290010 ti: c00000000b738000 task.ti: c00000000b738000
>> NIP: c000000000047df4 LR: c0000000000f9e58 CTR: c00000000010f180
>> REGS: c00000000b73b570 TRAP: 0300 Tainted: G L X (4.4.140+)
>> MSR: 8000000000009033 <SF,EE,ME,IR,DR,RI,LE> CR: 22004484 XER: 20000000
>> CFAR: c000000000008500 DAR: 000007a450000000 DSISR: 40000000 SOFTE: 0
>> GPR00: c0000000000f9e58 c00000000b73b7f0 c000000000f09a00 000000000000001a
>> GPR04: c00007f3bf774c90 0000000000000004 c000000000eb9a00 0000000000000800
>> GPR08: 0000000000000804 000007a450000000 c000000000fa9a00 c00007ffb169ca20
>> GPR12: 0000000022004482 c00000000fa12c00 c00007f3a0ea97a8 0000000000000000
>> GPR16: c00007f3a0ea9a50 c00000000b73bd60 0000000000000118 000000000001fe80
>> GPR20: 0000000000000118 0000000000000000 c000000000b8c980 00000000000000d0
>> GPR24: 000007ffb0b10000 c00007ffb169c980 0000000000000000 c000000000b8c980
>> GPR28: 0000000000000004 c00007ffb169c980 000000000000001a c00007ffb169c980
>> NIP [c000000000047df4] smp_send_reschedule+0x24/0x80
>> LR [c0000000000f9e58] resched_curr+0x138/0x160
>> Call Trace:
>> [c00000000b73b7f0] [c0000000000f9e58] resched_curr+0x138/0x160 (unreliable)
>> [c00000000b73b820] [c0000000000fb538] check_preempt_curr+0xc8/0xf0
>> [c00000000b73b850] [c0000000000fb598] ttwu_do_wakeup+0x38/0x150
>> [c00000000b73b890] [c0000000000fc9c4] try_to_wake_up+0x224/0x4d0
>> [c00000000b73b900] [c00000000011ef34] __wake_up_common+0x94/0x100
>> [c00000000b73b960] [c00000000034a78c] ep_poll_callback+0xac/0x1c0
>> [c00000000b73b9b0] [c00000000011ef34] __wake_up_common+0x94/0x100
>> [c00000000b73ba10] [c00000000011f810] __wake_up_sync_key+0x70/0xa0
>> [c00000000b73ba60] [c00000000067c3e8] sock_def_readable+0x58/0xa0
>> [c00000000b73ba90] [c0000000007848ac] unix_stream_sendmsg+0x2dc/0x4c0
>> [c00000000b73bb70] [c000000000675a38] sock_sendmsg+0x68/0xa0
>> [c00000000b73bba0] [c00000000067673c] ___sys_sendmsg+0x2cc/0x2e0
>> [c00000000b73bd30] [c000000000677dbc] __sys_sendmsg+0x5c/0xc0
>> [c00000000b73bdd0] [c0000000006789bc] SyS_socketcall+0x36c/0x3f0
>> [c00000000b73be30] [c000000000009488] system_call+0x3c/0x100
>> Instruction dump:
>> 4e800020 60000000 60420000 3c4c00ec 38421c30 7c0802a6 f8010010 60000000
>> 3d42000a e92ab420 2fa90000 4dde0020 <e9290000> 2fa90000 419e0044 7c0802a6
>> ---[ end trace a6d1dd4bab5f8253 ]---
>>
>> as array index overflow is not checked for while setting up crash memory
>> ranges causing memory corruption. To resolve this issue, resize crash
>> memory ranges array on hitting array size limit.
>>
>> But without a hard limit on the number of crash memory ranges, there is
>> a possibility of program headers count overflow in the /proc/vmcore ELF
>> file while exporting each of this memory ranges as PT_LOAD segments. To
>> reduce the likelihood of such scenario, fold adjacent memory ranges to
>> minimize the total number of crash memory ranges.
>>
>> Fixes: 2df173d9e85d ("fadump: Initialize elfcore header and add PT_LOAD program headers.")
>> Cc: stable at vger.kernel.org
>> Cc: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
>> Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
>> ---
>> arch/powerpc/include/asm/fadump.h | 2 +
>> arch/powerpc/kernel/fadump.c | 63 ++++++++++++++++++++++++++++++++++---
>> 2 files changed, 59 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/fadump.h b/arch/powerpc/include/asm/fadump.h
>> index 5a23010..ff708b3 100644
>> --- a/arch/powerpc/include/asm/fadump.h
>> +++ b/arch/powerpc/include/asm/fadump.h
>> @@ -196,7 +196,7 @@ struct fadump_crash_info_header {
>> };
>>
>> /* Crash memory ranges */
>> -#define INIT_CRASHMEM_RANGES (INIT_MEMBLOCK_REGIONS + 2)
>> +#define INIT_CRASHMEM_RANGES INIT_MEMBLOCK_REGIONS
>>
>> struct fad_crash_memory_ranges {
>> unsigned long long base;
>> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
>> index 07e8396..1c1df4f 100644
>> --- a/arch/powerpc/kernel/fadump.c
>> +++ b/arch/powerpc/kernel/fadump.c
>> @@ -47,7 +47,9 @@ static struct fadump_mem_struct fdm;
>> static const struct fadump_mem_struct *fdm_active;
>>
>> static DEFINE_MUTEX(fadump_mutex);
>> -struct fad_crash_memory_ranges crash_memory_ranges[INIT_CRASHMEM_RANGES];
>> +struct fad_crash_memory_ranges init_crash_memory_ranges[INIT_CRASHMEM_RANGES];
>> +int max_crash_mem_ranges = INIT_CRASHMEM_RANGES;
>> +struct fad_crash_memory_ranges *crash_memory_ranges = init_crash_memory_ranges;
>> int crash_mem_ranges;
>>
>> /* Scan the Firmware Assisted dump configuration details. */
>> @@ -871,14 +873,65 @@ static int __init process_fadump(const struct fadump_mem_struct *fdm_active)
>> static inline void fadump_add_crash_memory(unsigned long long base,
>> unsigned long long end)
>> {
>> + u64 start, size;
>> + bool is_adjacent = false;
>> +
>> if (base == end)
>> return;
>>
>> + /*
>> + * Fold adjacent memory ranges to bring down the memory ranges/
>> + * PT_LOAD segments count.
>> + */
>> + if (crash_mem_ranges) {
>> + start = crash_memory_ranges[crash_mem_ranges-1].base;
>> + size = crash_memory_ranges[crash_mem_ranges-1].size;
>> +
>> + if ((start + size) == base)
>> + is_adjacent = true;
>> + }
>> +
>> + if (!is_adjacent) {
>> + /* resize the array on reaching the limit */
>> + if (crash_mem_ranges == max_crash_mem_ranges) {
>> + u64 old_size, new_max;
>> + struct fad_crash_memory_ranges *new_array;
>> +
>> + old_size = max_crash_mem_ranges;
>> + old_size *= sizeof(struct fad_crash_memory_ranges);
>> +
>> + new_max = max_crash_mem_ranges + INIT_CRASHMEM_RANGES;
>> + size = new_max * sizeof(struct fad_crash_memory_ranges);
>> +
>> + pr_debug("Resizing crash memory ranges count from %d to %d\n",
>> + max_crash_mem_ranges, new_max);
>> +
>> + new_array = kmalloc(size, GFP_KERNEL);
>> + if (new_array == NULL) {
>> + pr_warn("Insufficient memory for setting up crash memory ranges\n");
>> + return;
> Looks like we still going ahead with fadump registration in this case.
> This will give us partial dump. Should we not fail fadump registration
> if we are not able to cover all the crash memory ranges ??
I preferred to register even if we failed to setup all memory ranges as
partial dump
is better than no dump at all. As that dump may not be useful always,
should I just
error out to avoid false expectations?
> Also alongwith this change, Should we also double the initial array size
> (e.g. INIT_CRASHMEM_RANGES * 2) to reduce our chances to go for memory
> allocation ?
Agreed that doubling the static array size reduces the likelihood of the
need for
dynamic array resizing. Will do that.
Nonetheless, if we get to the point where 2K memory allocation fails on
a system
with so many memory ranges, it is likely that the kernel has some basic
problems
to deal with first :)
Thanks
Hari
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