powerpc allocates a text poke area of one page that is used by patch_instruction() to modify read-only text when STRICT_KERNEL_RWX is enabled.
patch_instruction() is only designed for instructions, so writing data using the text poke area can only happen 4 bytes at a time - each with a page map/unmap, pte flush and syncs. This patch introduces patch_memory(), implementing the same interface as memcpy(), similar to x86's text_poke() and s390's s390_kernel_write(). patch_memory() only needs to map the text poke area once, unless the write would cross a page boundary. Signed-off-by: Russell Currey <rus...@russell.cc> --- Sorry I took so long to post this. Some discussion here: https://github.com/linuxppc/issues/issues/375 arch/powerpc/include/asm/code-patching.h | 1 + arch/powerpc/lib/code-patching.c | 73 ++++++++++++++++++++++++ 2 files changed, 74 insertions(+) diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h index 4ba834599c4d..604211d8380c 100644 --- a/arch/powerpc/include/asm/code-patching.h +++ b/arch/powerpc/include/asm/code-patching.h @@ -31,6 +31,7 @@ int create_cond_branch(struct ppc_inst *instr, const u32 *addr, int patch_branch(u32 *addr, unsigned long target, int flags); int patch_instruction(u32 *addr, struct ppc_inst instr); int raw_patch_instruction(u32 *addr, struct ppc_inst instr); +void *patch_memory(void *dest, const void *src, size_t size); static inline unsigned long patch_site_addr(s32 *site) { diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index c5ed98823835..3a566d756ccc 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -17,6 +17,7 @@ #include <asm/code-patching.h> #include <asm/setup.h> #include <asm/inst.h> +#include <asm/cacheflush.h> static int __patch_instruction(u32 *exec_addr, struct ppc_inst instr, u32 *patch_addr) { @@ -178,6 +179,73 @@ static int do_patch_instruction(u32 *addr, struct ppc_inst instr) return err; } + +static int do_patch_memory(void *dest, const void *src, size_t size, unsigned long poke_addr) +{ + unsigned long patch_addr = poke_addr + offset_in_page(dest); + + if (map_patch_area(dest, poke_addr)) { + pr_warn("failed to map %lx\n", poke_addr); + return -1; + } + + memcpy((u8 *)patch_addr, src, size); + + flush_icache_range(patch_addr, size); + + if (unmap_patch_area(poke_addr)) { + pr_warn("failed to unmap %lx\n", poke_addr); + return -1; + } + + return 0; +} + +/** + * patch_memory - write data using the text poke area + * + * @dest: destination address + * @src: source address + * @size: size in bytes + * + * like memcpy(), but using the text poke area. No atomicity guarantees. + * Do not use for instructions, use patch_instruction() instead. + * Handles crossing page boundaries, though you shouldn't need to. + * + * Return value: + * @dest + **/ +void *patch_memory(void *dest, const void *src, size_t size) +{ + size_t bytes_written, write_size; + unsigned long text_poke_addr; + unsigned long flags; + + // If the poke area isn't set up, it's early boot and we can just memcpy. + if (!this_cpu_read(text_poke_area)) + return memcpy(dest, src, size); + + local_irq_save(flags); + text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr; + + for (bytes_written = 0; + bytes_written < size; + bytes_written += write_size) { + // Write as much as possible without crossing a page boundary. + write_size = min(size - bytes_written, + PAGE_SIZE - offset_in_page(dest + bytes_written)); + + if (do_patch_memory(dest + bytes_written, + src + bytes_written, + write_size, + text_poke_addr)) + break; + } + + local_irq_restore(flags); + + return dest; +} #else /* !CONFIG_STRICT_KERNEL_RWX */ static int do_patch_instruction(u32 *addr, struct ppc_inst instr) @@ -185,6 +253,11 @@ static int do_patch_instruction(u32 *addr, struct ppc_inst instr) return raw_patch_instruction(addr, instr); } +void *patch_memory(void *dest, const void *src, size_t size) +{ + return memcpy(dest, src, size); +} + #endif /* CONFIG_STRICT_KERNEL_RWX */ int patch_instruction(u32 *addr, struct ppc_inst instr) -- 2.34.1
