Re: [PATCH v2] riscv: Fix memblock reservation for device tree blob

[Paul Walmsley]

On Fri, 27 Sep 2019, Albert Ou wrote:

> This fixes an error with how the FDT blob is reserved in memblock.
> An incorrect physical address calculation exposed the FDT header to
> unintended corruption, which typically manifested with of_fdt_raw_init()
> faulting during late boot after fdt_totalsize() returned a wrong value.
> Systems with smaller physical memory sizes more frequently trigger this
> issue, as the kernel is more likely to allocate from the DMA32 zone
> where bbl places the DTB after the kernel image.
> 
> Commit 671f9a3e2e24 ("RISC-V: Setup initial page tables in two stages")
> changed the mapping of the DTB to reside in the fixmap area.
> Consequently, early_init_fdt_reserve_self() cannot be used anymore in
> setup_bootmem() since it relies on __pa() to derive a physical address,
> which does not work with dtb_early_va that is no longer a valid kernel
> logical address.
> 
> The reserved[0x1] region shows the effect of the pointer underflow
> resulting from the __pa(initial_boot_params) offset subtraction:
> 
> [    0.000000] MEMBLOCK configuration:
> [    0.000000]  memory size = 0x000000001fe00000 reserved size = 0x0000000000a2e514
> [    0.000000]  memory.cnt  = 0x1
> [    0.000000]  memory[0x0]     [0x0000000080200000-0x000000009fffffff], 0x000000001fe00000 bytes flags: 0x0
> [    0.000000]  reserved.cnt  = 0x2
> [    0.000000]  reserved[0x0]   [0x0000000080200000-0x0000000080c2dfeb], 0x0000000000a2dfec bytes flags: 0x0
> [    0.000000]  reserved[0x1]   [0xfffffff080100000-0xfffffff080100527], 0x0000000000000528 bytes flags: 0x0
> 
> With the fix applied:
> 
> [    0.000000] MEMBLOCK configuration:
> [    0.000000]  memory size = 0x000000001fe00000 reserved size = 0x0000000000a2e514
> [    0.000000]  memory.cnt  = 0x1
> [    0.000000]  memory[0x0]     [0x0000000080200000-0x000000009fffffff], 0x000000001fe00000 bytes flags: 0x0
> [    0.000000]  reserved.cnt  = 0x2
> [    0.000000]  reserved[0x0]   [0x0000000080200000-0x0000000080c2dfeb], 0x0000000000a2dfec bytes flags: 0x0
> [    0.000000]  reserved[0x1]   [0x0000000080e00000-0x0000000080e00527], 0x0000000000000528 bytes flags: 0x0
> 
> Fixes: 671f9a3e2e24 ("RISC-V: Setup initial page tables in two stages")
> Signed-off-by: Albert Ou <aou@xxxxxxxxxxxxxxxxx>

Thanks, queued for v5.4-rc.  Welcome back Albert :-)


- Paul