Re: [PATCH bpf-next v3 2/3] riscv: implement a memset like function for text

[Pu Lehui <pulehui@huawei.com>]

On 2023/8/29 0:59, Puranjay Mohan wrote:
> The BPF JIT needs to write invalid instructions to RX regions of memory to
> invalidate removed BPF programs. This needs a function like memset() that
> can work with RX memory.
> 
> Implement patch_text_set_nosync() which is similar to text_poke_set() of
> x86.
> 
> Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> ---
>   arch/riscv/include/asm/patch.h |  1 +
>   arch/riscv/kernel/patch.c      | 77 ++++++++++++++++++++++++++++++++++
>   2 files changed, 78 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/patch.h b/arch/riscv/include/asm/patch.h
> index 63c98833d510..e88b52d39eac 100644
> --- a/arch/riscv/include/asm/patch.h
> +++ b/arch/riscv/include/asm/patch.h
> @@ -7,6 +7,7 @@
>   #define _ASM_RISCV_PATCH_H
>   
>   int patch_text_nosync(void *addr, const void *insns, size_t len);
> +int patch_text_set_nosync(void *addr, u8 c, size_t len);
>   int patch_text(void *addr, u32 *insns, int ninsns);
>   
>   extern int riscv_patch_in_stop_machine;
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 2c97e246f4dc..13ee7bf589a1 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -6,6 +6,7 @@
>   #include <linux/spinlock.h>
>   #include <linux/mm.h>
>   #include <linux/memory.h>
> +#include <linux/string.h>
>   #include <linux/uaccess.h>
>   #include <linux/stop_machine.h>
>   #include <asm/kprobes.h>
> @@ -53,6 +54,39 @@ static void patch_unmap(int fixmap)
>   }
>   NOKPROBE_SYMBOL(patch_unmap);
>   
> +static int __patch_insn_set(void *addr, u8 c, size_t len)
> +{
> +	void *waddr = addr;
> +	bool across_pages = (((uintptr_t)addr & ~PAGE_MASK) + len) > PAGE_SIZE;
> +
> +	/*
> +	 * Only two pages can be mapped at a time for writing.
> +	 */
> +	if (len + offset_in_page(addr) > 2 * PAGE_SIZE)
> +		return -EINVAL;
> +	/*
> +	 * Before reaching here, it was expected to lock the text_mutex
> +	 * already, so we don't need to give another lock here and could
> +	 * ensure that it was safe between each cores.
> +	 */
> +	lockdep_assert_held(&text_mutex);
> +
> +	if (across_pages)
> +		patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
> +
> +	waddr = patch_map(addr, FIX_TEXT_POKE0);
> +
> +	memset(waddr, c, len);
> +
> +	patch_unmap(FIX_TEXT_POKE0);
> +
> +	if (across_pages)
> +		patch_unmap(FIX_TEXT_POKE1);
> +
> +	return 0;
> +}
> +NOKPROBE_SYMBOL(__patch_insn_set);
> +
>   static int __patch_insn_write(void *addr, const void *insn, size_t len)
>   {
>   	void *waddr = addr;
> @@ -95,6 +129,14 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
>   }
>   NOKPROBE_SYMBOL(__patch_insn_write);
>   #else
> +static int __patch_insn_set(void *addr, u8 c, size_t len)
> +{
> +	memset(addr, c, len);
> +
> +	return 0;
> +}
> +NOKPROBE_SYMBOL(__patch_insn_set);
> +
>   static int __patch_insn_write(void *addr, const void *insn, size_t len)
>   {
>   	return copy_to_kernel_nofault(addr, insn, len);
> @@ -102,6 +144,41 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
>   NOKPROBE_SYMBOL(__patch_insn_write);
>   #endif /* CONFIG_MMU */
>   
> +static int patch_insn_set(void *addr, u8 c, size_t len)
> +{
> +	size_t patched = 0;
> +	size_t size;
> +	int ret = 0;
> +
> +	/*
> +	 * __patch_insn_set() can only work on 2 pages at a time so call it in a
> +	 * loop with len <= 2 * PAGE_SIZE.
> +	 */
> +	while (patched < len && !ret) {
> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
> +		ret = __patch_insn_set(addr + patched, c, size);
> +
> +		patched += size;
> +	}
> +
> +	return ret;
> +}
> +NOKPROBE_SYMBOL(patch_insn_set);
> +
> +int patch_text_set_nosync(void *addr, u8 c, size_t len)
> +{
> +	u32 *tp = addr;
> +	int ret;
> +
> +	ret = patch_insn_set(tp, c, len);
> +
> +	if (!ret)
> +		flush_icache_range((uintptr_t)tp, (uintptr_t)tp + len);
> +
> +	return ret;
> +}
> +NOKPROBE_SYMBOL(patch_text_set_nosync);
> +
>   static int patch_insn_write(void *addr, const void *insn, size_t len)
>   {
>   	size_t patched = 0;

Reviewed-by: Pu Lehui <pulehui@huawei.com>