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Message-ID: <89a39da0-1835-397a-caa2-d676764afd20@huawei.com>
Date: Tue, 29 Aug 2023 10:49:57 +0800
From: Pu Lehui <pulehui@...wei.com>
To: Puranjay Mohan <puranjay12@...il.com>, <paul.walmsley@...ive.com>,
<palmer@...belt.com>, <aou@...s.berkeley.edu>,
<conor.dooley@...rochip.com>, <ast@...nel.org>,
<daniel@...earbox.net>, <andrii@...nel.org>,
<martin.lau@...ux.dev>, <song@...nel.org>, <yhs@...com>,
<kpsingh@...nel.org>, <bjorn@...nel.org>, <bpf@...r.kernel.org>,
<linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 2/3] riscv: implement a memset like function
for text
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@...il.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@...wei.com>
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