Re: [Xen-devel] [PATCH v5 14/16] livepatch: Initial ARM32 support.

[Julien Grall <julien.grall@xxxxxxx>]

Hi Konrad,

On 21/09/2016 10:32, Konrad Rzeszutek Wilk wrote:
> The patch piggybacks on: livepatch: Initial ARM64 support, which
> brings up all of the necessary livepatch infrastructure pieces in.
>
> This patch adds three major pieces:
>
>  1) ELF relocations. ARM32 uses SHT_REL instead of SHT_RELA which
>     means the adddendum had to be extracted from within the
>     instruction. Which required parsing BL/BLX, B/BL<cond>,
>     MOVT, and MOVW instructions.
>
>     The code was written from scratch using the ARM ELF manual
>     (and the ARM Architecture Reference Manual)
>
>  2) Inserting an trampoline. We use the B (branch to address)
>     which uses an offset that is based on the PC value: PC + imm32.
>     Because we insert the branch at the start of the old function
>     we have to account for the instruction already being fetched
>     and subtract -8 from the delta (new_addr - old_addr). See
>     ARM DDI 0406C.c, see A2.3 (pg 45) and A8.8.18 pg (pg 334,335)
>
>  3) Allows the test-cases to be built under ARM 32.
>     The "livepatch: tests: Make them compile under ARM64"
>     put in the right infrastructure for it and we piggyback on it.
>
> Acked-by: Julien Grall <julien.grall@xxxxxxx>
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx> [for non-ARM parts]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>
> v2: First submission.
> v3: Use LIVEPATCH_ARCH_RANGE instead of NEGATIVE_32MB macro
>    -Use PATCH_INSN_SIZE instead of the value 4.
>    -Ditch the old_ptr local variable.
>    -Use 8 for evaluating the branch instead of 4. Based on ARM docs.
>    -NOP patch up to sizeof(opaque) % PATCH_INSN_SIZE (so 7 instructions).
>    -Don't mask 0x00FFFFF_E_ after shifting, instead mask by 0x00FFFFF_F_.
>     The reason is that offset is constructed by shifting by two the insn
>     (except the first two bytes) by left which meant we would have cleared
>     offset[2]! - and jumped to a location that was -4 bytes off.
>    -Update commit description to have -8 instead of -4 delta and also
>     include reference to spec.
> v4: Added Jan's Ack.
>    s/PATCH_INSN_SIZE/ARCH_PATCH_INSN_SIZE/
>    s/arch_livepatch_insn_len/livepatch_insn_len/
>    s/LIVEPATCH_ARCH_RANGE/ARCH_LIVEPATCH_RANGE/
> v5: Added Julien's Ack.
IHMO my ack should not have been retained given that ...

>    - Rebased on "livepatch: Drop _jmp from arch_livepatch_[apply,revert]_jmp"
>    - Added explanation for the usage of data cache and why we need to sync it.
... you also replace the clean_and_invalidate to the old_ptr by 
clean_and_invalidate to the new_ptr.
> diff --git a/xen/arch/arm/arm32/livepatch.c b/xen/arch/arm/arm32/livepatch.c
> index 80f9646..3f47326 100644
> --- a/xen/arch/arm/arm32/livepatch.c
> +++ b/xen/arch/arm/arm32/livepatch.c
> @@ -3,28 +3,303 @@
>   */
>
>  #include <xen/errno.h>
> +#include <xen/kernel.h>
>  #include <xen/lib.h>
>  #include <xen/livepatch_elf.h>
>  #include <xen/livepatch.h>
>
> +#include <asm/page.h>
> +#include <asm/livepatch.h>
> +
>  void arch_livepatch_apply(struct livepatch_func *func)
>  {
[...]

> +    /*
> +    * When we upload the payload, it will go through the data cache
> +    * (the region is cacheable). Until the data cache is cleaned, the data
> +    * may not reach the memory. And in the case the data and instruction cache
> +    * are separated, we may read invalid instruction from the memory because
> +    * the data cache have not yet synced with the memory. Hence sync it.
> +    */
> +    if ( func->new_addr )
> +        clean_and_invalidate_dcache_va_range(func->new_addr, func->new_size);
The clean_and_invalidate on the new_ptr needs to be add back here and ...

>  }
>
>  void arch_livepatch_revert(const struct livepatch_func *func)
>  {
> +    uint32_t *new_ptr;
> +    unsigned int i, len;
> +
> +    new_ptr = func->old_addr - (void *)_start + vmap_of_xen_text;
> +    len = livepatch_insn_len(func) / sizeof(uint32_t);
> +    for ( i = 0; i < len; i++ )
> +    {
> +        uint32_t insn;
> +
> +        memcpy(&insn, func->opaque + (i * sizeof(uint32_t)), 
> ARCH_PATCH_INSN_SIZE);
> +        /* PATCH! */
> +        *(new_ptr + i) = insn;
> +    }
here. See the comments on the ARM64 part (i.e patch #5).

>  }
Regards,

--
Julien Grall

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