5.4-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Lynch nathanl@linux.ibm.com
[ Upstream commit bd68ffce69f6cf8ddd3a3c32549d1d2275e49fc5 ]
dlpar_memory_remove_by_index() may access beyond the bounds of the drmem lmb array when the LMB lookup fails to match an entry with the given DRC index. When the search fails, the cursor is left pointing to &drmem_info->lmbs[drmem_info->n_lmbs], which is one element past the last valid entry in the array. The debug message at the end of the function then dereferences this pointer:
pr_debug("Failed to hot-remove memory at %llx\n", lmb->base_addr);
This was found by inspection and confirmed with KASAN:
pseries-hotplug-mem: Attempting to hot-remove LMB, drc index 1234 ================================================================== BUG: KASAN: slab-out-of-bounds in dlpar_memory+0x298/0x1658 Read of size 8 at addr c000000364e97fd0 by task bash/949
dump_stack_lvl+0xa4/0xfc (unreliable) print_report+0x214/0x63c kasan_report+0x140/0x2e0 __asan_load8+0xa8/0xe0 dlpar_memory+0x298/0x1658 handle_dlpar_errorlog+0x130/0x1d0 dlpar_store+0x18c/0x3e0 kobj_attr_store+0x68/0xa0 sysfs_kf_write+0xc4/0x110 kernfs_fop_write_iter+0x26c/0x390 vfs_write+0x2d4/0x4e0 ksys_write+0xac/0x1a0 system_call_exception+0x268/0x530 system_call_vectored_common+0x15c/0x2ec
Allocated by task 1: kasan_save_stack+0x48/0x80 kasan_set_track+0x34/0x50 kasan_save_alloc_info+0x34/0x50 __kasan_kmalloc+0xd0/0x120 __kmalloc+0x8c/0x320 kmalloc_array.constprop.0+0x48/0x5c drmem_init+0x2a0/0x41c do_one_initcall+0xe0/0x5c0 kernel_init_freeable+0x4ec/0x5a0 kernel_init+0x30/0x1e0 ret_from_kernel_user_thread+0x14/0x1c
The buggy address belongs to the object at c000000364e80000 which belongs to the cache kmalloc-128k of size 131072 The buggy address is located 0 bytes to the right of allocated 98256-byte region [c000000364e80000, c000000364e97fd0)
================================================================== pseries-hotplug-mem: Failed to hot-remove memory at 0
Log failed lookups with a separate message and dereference the cursor only when it points to a valid entry.
Signed-off-by: Nathan Lynch nathanl@linux.ibm.com Fixes: 51925fb3c5c9 ("powerpc/pseries: Implement memory hotplug remove in the kernel") Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20231114-pseries-memhp-fixes-v1-1-fb8f2bb7c557@linux.ibm.... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/platforms/pseries/hotplug-memory.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c index 03fb4669a1f0..23dc59e40edc 100644 --- a/arch/powerpc/platforms/pseries/hotplug-memory.c +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c @@ -510,14 +510,15 @@ static int dlpar_memory_remove_by_index(u32 drc_index) } }
- if (!lmb_found) + if (!lmb_found) { + pr_debug("Failed to look up LMB for drc index %x\n", drc_index); rc = -EINVAL; - - if (rc) + } else if (rc) { pr_debug("Failed to hot-remove memory at %llx\n", lmb->base_addr); - else + } else { pr_debug("Memory at %llx was hot-removed\n", lmb->base_addr); + }
return rc; }