CVE: CVE-2022-49851
Published: 2025-05-01
Description: In the Linux kernel, the following vulnerability has been resolved:

riscv: fix reserved memory setup

Currently, RISC-V sets up reserved memory using the "early" copy of the
device tree. As a result, when trying to get a reserved memory region
using of_reserved_mem_lookup(), the pointer to reserved memory regions
is using the early, pre-virtual-memory address which causes a kernel
panic when trying to use the buffer's name:

 Unable to handle kernel paging request at virtual address[PII_REDACTED]1c31ac
 Oops [#1]
 Modules linked in:
 CPU: 0 PID: 0 Comm: swapper Not tainted 6.0.0-rc1-00001-g0d9d6953d834 #1
 Hardware name: Microchip PolarFire-SoC Icicle Kit (DT)
 epc : string+0x4a/0xea
  ra : vsnprintf+0x1e4/0x336
 epc : ffffffff80335ea0 ra : ffffffff80338936 sp : ffffffff81203be0
  gp : ffffffff812e0a98 tp : ffffffff8120de40 t0 : [PII_REDACTED]
  t1 : ffffffff81203e28 t2 :[PII_REDACTED]203a46 s0 : ffffffff81203c20
  s1 : ffffffff81203e28 a0 : ffffffff81203d22 a1 : [PII_REDACTED]
  a2 : ffffffff81203d08 a3 :[PII_REDACTED]203d21 a4 : ffffffffffffffff
  a5 :[PII_REDACTED]1c31ac a6 : ffff0a00ffffff04 a7 : ffffffffffffffff
  s2 : ffffffff81203d08 s3 : ffffffff81203d00 s4 : [PII_REDACTED]
  s5 : ffffffff000000ff s6 :[PII_REDACTED]ffffff s7 : 00000000ffffff00
  s8 : ffffffff80d9821a s9 : ffffffff81203d22 s10: [PII_REDACTED]
  s11: ffffffff80d9821c t3 : ffffffff812f3617 t4 : ffffffff812f3617
  t5 : ffffffff812f3618 t6 : ffffffff81203d08
 status: [PII_REDACTED] badaddr:[PII_REDACTED]1c31ac cause:[PII_REDACTED]00000d
 [<ffffffff80338936>] vsnprintf+0x1e4/0x336
 [<ffffffff80055ae2>] vprintk_store+0xf6/0x344
 [<ffffffff80055d86>] vprintk_emit+0x56/0x192
 [<ffffffff80055ed8>] vprintk_default+0x16/0x1e
 [<ffffffff800563d2>] vprintk+0x72/0x80
 [<ffffffff806813b2>] _printk+0x36/0x50
 [<ffffffff8068af48>] print_reserved_mem+0x1c/0x24
 [<ffffffff808057ec>] paging_init+0x528/0x5bc
 [<ffffffff808031ae>] setup_arch+0xd0/0x592
 [<ffffffff8080070e>] start_kernel+0x82/0x73c

early_init_fdt_scan_reserved_mem() takes no arguments as it operates on
initial_boot_params, which is populated by early_init_dt_verify(). On
RISC-V, early_init_dt_verify() is called twice. Once, directly, in
setup_arch() if CONFIG_BUILTIN_DTB is not enabled and once indirectly,
very early in the boot process, by parse_dtb() when it calls
early_init_dt_scan_nodes().

This first call uses dtb_early_va to set initial_boot_params, which is
not usable later in the boot process when
early_init_fdt_scan_reserved_mem() is called. On arm64 for example, the
corresponding call to early_init_dt_scan_nodes() uses fixmap addresses
and doesn't suffer the same fate.

Move early_init_fdt_scan_reserved_mem() further along the boot sequence,
after the direct call to early_init_dt_verify() in setup_arch() so that
the names use the correct virtual memory addresses. The above supposed
that CONFIG_BUILTIN_DTB was not set, but should work equally in the case
where it is - unflatted_and_copy_device_tree() also updates
initial_boot_params.
CVSS Score: 7.1 (HIGH)
CWE: CWE-125
References: https://git.kernel.org/stable/c/50e63dd8ed92045eb70a72d7ec725488320fb68b; https://git.kernel.org/stable/c/518e49f0590de66555503aabe199ba8d3f2e24ac; https://git.kernel.org/stable/c/93598deb101540c4f9e7de15099ea8255b965fc2