Re: [PATCH] resource,kexec: walk_system_ram_res_rev must retain resource flags

[Baoquan He <bhe@redhat.com>]

HI Gregory,

On 10/17/24 at 03:03pm, Gregory Price wrote:
> walk_system_ram_res_rev() erroneously discards resource flags when
> passing the information to the callback.
> 
> This causes systems with IORESOURCE_SYSRAM_DRIVER_MANAGED memory to
> have these resources selected during kexec to store kexec buffers
> if that memory happens to be at placed above normal system ram.

Sorry about that. I haven't checked IORESOURCE_SYSRAM_DRIVER_MANAGED
memory carefully, wondering if res could be set as
'IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY' plus
IORESOURCE_SYSRAM_DRIVER_MANAGED in iomem_resource tree.

Anyway, the change in this patch is certainly better. Thanks.

Acked-by: Baoquan He <bhe@redhat.com>

> 
> This leads to undefined behavior after reboot. If the kexec buffer
> is never touched, nothing happens. If the kexec buffer is touched,
> it could lead to a crash (like below) or undefined behavior.
> 
> Tested on a system with CXL memory expanders with driver managed
> memory, TPM enabled, and CONFIG_IMA_KEXEC=y. Adding printk's
> showed the flags were being discarded and as a result the check
> for IORESOURCE_SYSRAM_DRIVER_MANAGED passes.
> 
> find_next_iomem_res: name(System RAM (kmem))
> 		     start(10000000000)
> 		     end(1034fffffff)
> 		     flags(83000200)
> 
> locate_mem_hole_top_down: start(10000000000) end(1034fffffff) flags(0)
> 
> [.] BUG: unable to handle page fault for address: ffff89834ffff000
> [.] #PF: supervisor read access in kernel mode
> [.] #PF: error_code(0x0000) - not-present page
> [.] PGD c04c8bf067 P4D c04c8bf067 PUD c04c8be067 PMD 0
> [.] Oops: 0000 [#1] SMP
> [.] RIP: 0010:ima_restore_measurement_list+0x95/0x4b0
> [.] RSP: 0018:ffffc900000d3a80 EFLAGS: 00010286
> [.] RAX: 0000000000001000 RBX: 0000000000000000 RCX: ffff89834ffff000
> [.] RDX: 0000000000000018 RSI: ffff89834ffff000 RDI: ffff89834ffff018
> [.] RBP: ffffc900000d3ba0 R08: 0000000000000020 R09: ffff888132b8a900
> [.] R10: 4000000000000000 R11: 000000003a616d69 R12: 0000000000000000
> [.] R13: ffffffff8404ac28 R14: 0000000000000000 R15: ffff89834ffff000
> [.] FS:  0000000000000000(0000) GS:ffff893d44640000(0000) knlGS:0000000000000000
> [.] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [.] ata5: SATA link down (SStatus 0 SControl 300)
> [.] CR2: ffff89834ffff000 CR3: 000001034d00f001 CR4: 0000000000770ef0
> [.] PKRU: 55555554
> [.] Call Trace:
> [.]  <TASK>
> [.]  ? __die+0x78/0xc0
> [.]  ? page_fault_oops+0x2a8/0x3a0
> [.]  ? exc_page_fault+0x84/0x130
> [.]  ? asm_exc_page_fault+0x22/0x30
> [.]  ? ima_restore_measurement_list+0x95/0x4b0
> [.]  ? template_desc_init_fields+0x317/0x410
> [.]  ? crypto_alloc_tfm_node+0x9c/0xc0
> [.]  ? init_ima_lsm+0x30/0x30
> [.]  ima_load_kexec_buffer+0x72/0xa0
> [.]  ima_init+0x44/0xa0
> [.]  __initstub__kmod_ima__373_1201_init_ima7+0x1e/0xb0
> [.]  ? init_ima_lsm+0x30/0x30
> [.]  do_one_initcall+0xad/0x200
> [.]  ? idr_alloc_cyclic+0xaa/0x110
> [.]  ? new_slab+0x12c/0x420
> [.]  ? new_slab+0x12c/0x420
> [.]  ? number+0x12a/0x430
> [.]  ? sysvec_apic_timer_interrupt+0xa/0x80
> [.]  ? asm_sysvec_apic_timer_interrupt+0x16/0x20
> [.]  ? parse_args+0xd4/0x380
> [.]  ? parse_args+0x14b/0x380
> [.]  kernel_init_freeable+0x1c1/0x2b0
> [.]  ? rest_init+0xb0/0xb0
> [.]  kernel_init+0x16/0x1a0
> [.]  ret_from_fork+0x2f/0x40
> [.]  ? rest_init+0xb0/0xb0
> [.]  ret_from_fork_asm+0x11/0x20
> [.]  </TASK>
> 
> Link: https://lore.kernel.org/all/20231114091658.228030-1-bhe@redhat.com/
> Fixes: 7acf164b259d ("resource: add walk_system_ram_res_rev()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Gregory Price <gourry@gourry.net>
> ---
>  kernel/resource.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index b730bd28b422..4101016e8b20 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -459,9 +459,7 @@ int walk_system_ram_res_rev(u64 start, u64 end, void *arg,
>  			rams_size += 16;
>  		}
>  
> -		rams[i].start = res.start;
> -		rams[i++].end = res.end;
> -
> +		rams[i++] = res;
>  		start = res.end + 1;
>  	}
>  
> -- 
> 2.43.0
>