linux-kernel - Re: [PATCH 1/2] riscv: Fix crash during early errata patching

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Date:   Thu, 22 Sep 2022 09:31:56 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Samuel Holland <samuel@...lland.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org
Cc:     Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] riscv: Fix crash during early errata patching

Hi Samuel,

On 9/22/22 07:47, Samuel Holland wrote:
> The patch function for the T-Head PBMT errata calls __pa_symbol() before
> relocation. This crashes when CONFIG_DEBUG_VIRTUAL is enabled, because
> __pa_symbol() forwards to __phys_addr_symbol(), and __phys_addr_symbol()
> checks against the absolute kernel start/end address.
>
> Fix this by directly using the underlying kernel_mapping_va_to_pa().


I'd rather fix __phys_addr_symbol so that we can use __pa_symbol and 
then take advantage of the address range check. Instead of using _end in 
phys_addr_symbol, we have access to the size of the kernel mapping, so 
we could do something like that:

diff --git a/arch/riscv/mm/physaddr.c b/arch/riscv/mm/physaddr.c
index f981b1f95fa0..150691aef058 100644
--- a/arch/riscv/mm/physaddr.c
+++ b/arch/riscv/mm/physaddr.c
@@ -22,7 +22,7 @@ EXPORT_SYMBOL(__virt_to_phys);
  phys_addr_t __phys_addr_symbol(unsigned long x)
  {
         unsigned long kernel_start = kernel_map.virt_addr;
-       unsigned long kernel_end = (unsigned long)_end;
+       unsigned long kernel_end = kernel_map.virt_addr + kernel_map.size;

         /*
          * Boundary checking aginst the kernel image mapping.

Thanks,

Alex

>
> Fixes: a35707c3d850 ("riscv: add memory-type errata for T-Head")
> Signed-off-by: Samuel Holland <samuel@...lland.org>
> ---
>
>   arch/riscv/errata/thead/errata.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index 202c83f677b2..83174f13783e 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -76,8 +76,9 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al
>   		if (cpu_req_errata & tmp) {
>   			/* On vm-alternatives, the mmu isn't running yet */
>   			if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
> -				memcpy((void *)__pa_symbol(alt->old_ptr),
> -				       (void *)__pa_symbol(alt->alt_ptr), alt->alt_len);
> +				memcpy((void *)kernel_mapping_va_to_pa((unsigned long)alt->old_ptr),
> +				       (void *)kernel_mapping_va_to_pa((unsigned long)alt->alt_ptr),
> +				       alt->alt_len);
>   			else
>   				patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
>   		}