Patch "powerpc/pseries/memhp: Fix access beyond end of drmem array" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    powerpc/pseries/memhp: Fix access beyond end of drmem array

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-pseries-memhp-fix-access-beyond-end-of-drmem.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 471d0e098c9ee559934bd80488e1c116ab7a6e93
Author: Nathan Lynch <nathanl@xxxxxxxxxxxxx>
Date:   Tue Nov 14 11:01:53 2023 -0600

    powerpc/pseries/memhp: Fix access beyond end of drmem array
    
    [ 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@xxxxxxxxxxxxx>
    Fixes: 51925fb3c5c9 ("powerpc/pseries: Implement memory hotplug remove in the kernel")
    Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
    Link: https://msgid.link/20231114-pseries-memhp-fixes-v1-1-fb8f2bb7c557@xxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index aa4042dcd6d4..4adca5b61dab 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -435,14 +435,15 @@ 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;
 }




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