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puranjaymohanpalmer-dabbelt
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riscv: implement a memset like function for text
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> Reviewed-by: Pu Lehui <pulehui@huawei.com> Acked-by: Björn Töpel <bjorn@kernel.org> Tested-by: Björn Töpel <bjorn@rivosinc.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/r/20230831131229.497941-4-puranjay12@gmail.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
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arch/riscv/include/asm/patch.h

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@@ -7,6 +7,7 @@
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#define _ASM_RISCV_PATCH_H
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int patch_text_nosync(void *addr, const void *insns, size_t len);
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int patch_text_set_nosync(void *addr, u8 c, size_t len);
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int patch_text(void *addr, u32 *insns, int ninsns);
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extern int riscv_patch_in_stop_machine;

arch/riscv/kernel/patch.c

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@@ -6,6 +6,7 @@
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#include <linux/spinlock.h>
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#include <linux/mm.h>
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#include <linux/memory.h>
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#include <linux/string.h>
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#include <linux/uaccess.h>
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#include <linux/stop_machine.h>
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#include <asm/kprobes.h>
@@ -53,6 +54,39 @@ static void patch_unmap(int fixmap)
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}
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NOKPROBE_SYMBOL(patch_unmap);
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static int __patch_insn_set(void *addr, u8 c, size_t len)
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{
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void *waddr = addr;
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bool across_pages = (((uintptr_t)addr & ~PAGE_MASK) + len) > PAGE_SIZE;
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/*
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* Only two pages can be mapped at a time for writing.
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*/
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if (len + offset_in_page(addr) > 2 * PAGE_SIZE)
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return -EINVAL;
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/*
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* Before reaching here, it was expected to lock the text_mutex
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* already, so we don't need to give another lock here and could
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* ensure that it was safe between each cores.
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*/
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lockdep_assert_held(&text_mutex);
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if (across_pages)
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patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
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waddr = patch_map(addr, FIX_TEXT_POKE0);
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memset(waddr, c, len);
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patch_unmap(FIX_TEXT_POKE0);
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if (across_pages)
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patch_unmap(FIX_TEXT_POKE1);
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return 0;
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}
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NOKPROBE_SYMBOL(__patch_insn_set);
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static int __patch_insn_write(void *addr, const void *insn, size_t len)
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{
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void *waddr = addr;
@@ -95,13 +129,56 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
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}
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NOKPROBE_SYMBOL(__patch_insn_write);
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#else
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static int __patch_insn_set(void *addr, u8 c, size_t len)
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{
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memset(addr, c, len);
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return 0;
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}
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NOKPROBE_SYMBOL(__patch_insn_set);
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static int __patch_insn_write(void *addr, const void *insn, size_t len)
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{
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return copy_to_kernel_nofault(addr, insn, len);
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}
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NOKPROBE_SYMBOL(__patch_insn_write);
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#endif /* CONFIG_MMU */
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static int patch_insn_set(void *addr, u8 c, size_t len)
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{
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size_t patched = 0;
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size_t size;
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int ret = 0;
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/*
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* __patch_insn_set() can only work on 2 pages at a time so call it in a
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* loop with len <= 2 * PAGE_SIZE.
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*/
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while (patched < len && !ret) {
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size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
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ret = __patch_insn_set(addr + patched, c, size);
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patched += size;
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}
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return ret;
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}
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NOKPROBE_SYMBOL(patch_insn_set);
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int patch_text_set_nosync(void *addr, u8 c, size_t len)
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{
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u32 *tp = addr;
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int ret;
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ret = patch_insn_set(tp, c, len);
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if (!ret)
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flush_icache_range((uintptr_t)tp, (uintptr_t)tp + len);
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return ret;
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}
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NOKPROBE_SYMBOL(patch_text_set_nosync);
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static int patch_insn_write(void *addr, const void *insn, size_t len)
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{
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size_t patched = 0;

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