Date:   Tue, 08 Oct 2019 16:35:38 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     aou@...s.berkeley.edu
CC:     anup@...infault.org, Paul Walmsley <paul.walmsley@...ive.com>,
        Anup Patel <Anup.Patel@....com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject:     Re: [PATCH] riscv: Fix memblock reservation for device tree blob

On Tue, 08 Oct 2019 16:31:17 PDT (-0700), aou@...s.berkeley.edu wrote:
> On 2019-10-08 15:38:15 -0700, Palmer Dabbelt <palmer@...ive.com> wrote:
>> On Fri, 20 Sep 2019 21:34:57 PDT (-0700), anup@...infault.org wrote:
>> > On Sat, Sep 21, 2019 at 6:30 AM Albert Ou <aou@...s.berkeley.edu> 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@...s.berkeley.edu>
>> >> ---
>> >>  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@...ts.infradead.org
>> >> http://lists.infradead.org/mailman/listinfo/linux-riscv
>> >
>> > This deserves to be stable kernel fix as well.
>> > You should add:
>> > Cc: stable@...r.kernel.org
>> > in your commit description.
>> >
>> > Apart from minor nits above.
>> >
>> > Reviewed-by: Anup Patel <anup@...infault.org>
>> >
>> > I tried this patch for both RV64 and RV32 on QEMU with
>> > Yocto rootfs.
>> >
>> > Tested-by: Anup Patel <anup@...infault.org>
>> >
>> > 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.

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