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

From: Palmer Dabbelt
Date: Tue Oct 08 2019 - 19:35:41 EST

On Tue, 08 Oct 2019 16:31:17 PDT (-0700), aou@xxxxxxxxxxxxxxxxx wrote:
On 2019-10-08 15:38:15 -0700, Palmer Dabbelt <palmer@xxxxxxxxxx> wrote:
On Fri, 20 Sep 2019 21:34:57 PDT (-0700), anup@xxxxxxxxxxxxxx wrote:
> On Sat, Sep 21, 2019 at 6:30 AM Albert Ou <aou@xxxxxxxxxxxxxxxxx> 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
>
> Thanks for catching this issue.
>
> Most of us did not notice this issue most likely because:
> 1. We generally have good enough RAM on QEMU and SiFive Unleashed
> 2. Most of people use OpenSBI FW_JUMP on QEMU and U-Boot on
> SiFive Unleashed to boot in Linux which places FDT quite far away
> from Linux kernel end
>
> Linux ARM64 kernel also uses FIXMAP to access FDT and over there
> as well early_init_fdt_reserve_self() is not used.
>
>>
>> Fixes: 671f9a3e2e24 ("RISC-V: Setup initial page tables in two stages")
>> Signed-off-by: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
>> ---
>> arch/riscv/mm/init.c | 13 ++++++++++++-
>> 1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index f0ba713..52d007c 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -11,6 +11,7 @@
>> #include <linux/swap.h>
>> #include <linux/sizes.h>
>> #include <linux/of_fdt.h>
>> +#include <linux/libfdt.h>
>>
>> #include <asm/fixmap.h>
>> #include <asm/tlbflush.h>
>> @@ -82,6 +83,8 @@ static void __init setup_initrd(void)
>> }
>> #endif /* CONFIG_BLK_DEV_INITRD */
>>
>> +static phys_addr_t __dtb_pa __initdata;
>
> May be dtb_early_pa will be more consistent name
> instead of __dtb_pa because it matches dtb_early_va
> used below.
>
>> +
>> void __init setup_bootmem(void)
>> {
>> struct memblock_region *reg;
>> @@ -117,7 +120,12 @@ void __init setup_bootmem(void)
>> setup_initrd();
>> #endif /* CONFIG_BLK_DEV_INITRD */
>>
>> - early_init_fdt_reserve_self();
>> + /*
>> + * Avoid using early_init_fdt_reserve_self() since __pa() does
>> + * not work for DTB pointers that are fixmap addresses
>> + */
>> + memblock_reserve(__dtb_pa, fdt_totalsize(dtb_early_va));
>> +
>> early_init_fdt_scan_reserved_mem();
>> memblock_allow_resize();
>> memblock_dump_all();
>> @@ -333,6 +341,7 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
>> "not use absolute addressing."
>> #endif
>>
>> +
>
> Please remove this newline addition.
>
>> asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>> {
>> uintptr_t va, end_va;
>> @@ -393,6 +402,8 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>
>> /* Save pointer to DTB for early FDT parsing */
>> dtb_early_va = (void *)fix_to_virt(FIX_FDT) + (dtb_pa & ~PAGE_MASK);
>> + /* Save physical address for memblock reservation */
>> + __dtb_pa = dtb_pa;
>> }
>>
>> static void __init setup_vm_final(void)
>> --
>> 2.7.4
>>
>>
>> _______________________________________________
>> linux-riscv mailing list
>> linux-riscv@xxxxxxxxxxxxxxxxxxx
>> http://lists.infradead.org/mailman/listinfo/linux-riscv
>
> This deserves to be stable kernel fix as well.
> You should add:
> Cc: stable@xxxxxxxxxxxxxxx
> in your commit description.
>
> Apart from minor nits above.
>
> Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
>
> I tried this patch for both RV64 and RV32 on QEMU with
> Yocto rootfs.
>
> Tested-by: Anup Patel <anup@xxxxxxxxxxxxxx>
>
> Regards,
> Anup

Albert: Do you plan on spinning a v2 of the patch set?


v2 was sent last week and has already been applied as
922b0375fc93fb1a20c5617e37c389c26bbccb70 by Paul.

Sorry about that.