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SubjectRe: [PATCH v2] riscv: Fix memblock reservation for device tree blob
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@eecs.berkeley.edu>

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


- Paul

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