[PATCH v2 1/6] powerpc/code-patching: Implement generic text patching function
Christophe Leroy
christophe.leroy at csgroup.eu
Tue Sep 27 16:40:06 AEST 2022
Le 26/09/2022 à 08:43, Benjamin Gray a écrit :
> Adds a generic text patching mechanism for patches of 1, 2, 4, or (64-bit) 8
> bytes. The patcher conditionally syncs the icache depending on if
> the content will be executed (as opposed to, e.g., read-only data).
>
> The `patch_instruction` function is reimplemented in terms of this
> more generic function. This generic implementation allows patching of
> arbitrary 64-bit data, whereas the original `patch_instruction` decided
> the size based on the 'instruction' opcode, so was not suitable for
> arbitrary data.
>
> Signed-off-by: Benjamin Gray <bgray at linux.ibm.com>
> ---
> arch/powerpc/include/asm/code-patching.h | 7 ++
> arch/powerpc/lib/code-patching.c | 90 +++++++++++++++++-------
> 2 files changed, 71 insertions(+), 26 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
> index 1c6316ec4b74..15efd8ab22da 100644
> --- a/arch/powerpc/include/asm/code-patching.h
> +++ b/arch/powerpc/include/asm/code-patching.h
> @@ -76,6 +76,13 @@ int create_cond_branch(ppc_inst_t *instr, const u32 *addr,
> int patch_branch(u32 *addr, unsigned long target, int flags);
> int patch_instruction(u32 *addr, ppc_inst_t instr);
> int raw_patch_instruction(u32 *addr, ppc_inst_t instr);
> +int __patch_memory(void *dest, unsigned long src, size_t size);
> +
> +#define patch_memory(addr, val) \
> +({ \
> + BUILD_BUG_ON(!__native_word(val)); \
> + __patch_memory(addr, (unsigned long) val, sizeof(val)); \
> +})
>
> 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 ad0cf3108dd0..9979380d55ef 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -15,20 +15,47 @@
> #include <asm/code-patching.h>
> #include <asm/inst.h>
>
> -static int __patch_instruction(u32 *exec_addr, ppc_inst_t instr, u32 *patch_addr)
> +static int __always_inline ___patch_memory(void *patch_addr,
> + unsigned long data,
> + void *prog_addr,
> + size_t size)
Could you reduce the number of lines ?
For instance:
static int __always_inline
___patch_memory(void *patch_addr, unsigned long data, void *prog_addr,
size_t size)
Also, 3 underscodes starts to be a lot too much, can we be a bit more
creative on the function name ?
> {
> - if (!ppc_inst_prefixed(instr)) {
> - u32 val = ppc_inst_val(instr);
> + switch (size) {
> + case 1:
> + __put_kernel_nofault(patch_addr, &data, u8, failed);
> + break;
> + case 2:
> + __put_kernel_nofault(patch_addr, &data, u16, failed);
> + break;
> + case 4:
> + __put_kernel_nofault(patch_addr, &data, u32, failed);
> + break;
> +#ifdef CONFIG_PPC64
> + case 8:
> + __put_kernel_nofault(patch_addr, &data, u64, failed);
> + break;
> +#endif
> + default:
> + unreachable();
> + }
>
> - __put_kernel_nofault(patch_addr, &val, u32, failed);
> - } else {
> - u64 val = ppc_inst_as_ulong(instr);
> + dcbst(patch_addr);
> + dcbst(patch_addr + size - 1); /* Last byte of data may cross a cacheline */
>
> - __put_kernel_nofault(patch_addr, &val, u64, failed);
> - }
> + mb(); /* sync */
> +
> + /* Flush on the EA that may be executed in case of a non-coherent icache */
> + icbi(prog_addr);
prog_addr is a misleading name ? Is that the address at which you
program it ? Is that the address the programs runs at ?
exec_addr was a lot more explicit as it clearly defines the address at
which the code is executed.
> +
> + /* Also flush the last byte of the instruction if it may be a
> + * prefixed instruction and we aren't assuming minimum 64-byte
> + * cacheline sizes
> + */
> + if (IS_ENABLED(CONFIG_PPC64) && L1_CACHE_BYTES < 64)
> + icbi(prog_addr + size - 1);
This doesn't exist today.
I'd rather have:
BUILD_BUG_ON(IS_ENABLED(CONFIG_PPC64) && L1_CACHE_BYTES < 64);
>
> - asm ("dcbst 0, %0; sync; icbi 0,%1; sync; isync" :: "r" (patch_addr),
> - "r" (exec_addr));
> + mb(); /* sync */
> + isync();
>
> return 0;
>
> @@ -38,7 +65,10 @@ static int __patch_instruction(u32 *exec_addr, ppc_inst_t instr, u32 *patch_addr
>
> int raw_patch_instruction(u32 *addr, ppc_inst_t instr)
> {
> - return __patch_instruction(addr, instr, addr);
> + if (ppc_inst_prefixed(instr))
> + return ___patch_memory(addr, ppc_inst_as_ulong(instr), addr, sizeof(u64));
> + else
> + return ___patch_memory(addr, ppc_inst_val(instr), addr, sizeof(u32));
> }
>
> #ifdef CONFIG_STRICT_KERNEL_RWX
> @@ -147,24 +177,22 @@ static void unmap_patch_area(unsigned long addr)
> flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> }
>
> -static int __do_patch_instruction(u32 *addr, ppc_inst_t instr)
> +static int __always_inline __do_patch_memory(void *dest, unsigned long src, size_t size)
> {
> int err;
> u32 *patch_addr;
> - unsigned long text_poke_addr;
> pte_t *pte;
> - unsigned long pfn = get_patch_pfn(addr);
> -
> - text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr & PAGE_MASK;
> - patch_addr = (u32 *)(text_poke_addr + offset_in_page(addr));
> + unsigned long text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr & PAGE_MASK;
> + unsigned long pfn = get_patch_pfn(dest);
>
> + patch_addr = (u32 *)(text_poke_addr + offset_in_page(dest));
Can we avoid this churn ?
Ok, you want to change 'addr' to 'dest', can we leave everything else as
is ?
Previously, there was a clear splitting of the function:
address preparation
blank line
MMU mapping
blank line
patching
blank line
MMU unmapping
Now the function seems disorganised and is less readable.
> pte = virt_to_kpte(text_poke_addr);
> __set_pte_at(&init_mm, text_poke_addr, pte, pfn_pte(pfn, PAGE_KERNEL), 0);
> /* See ptesync comment in radix__set_pte_at() */
> if (radix_enabled())
> asm volatile("ptesync": : :"memory");
>
> - err = __patch_instruction(addr, instr, patch_addr);
> + err = ___patch_memory(patch_addr, src, dest, size);
>
> pte_clear(&init_mm, text_poke_addr, pte);
> flush_tlb_kernel_range(text_poke_addr, text_poke_addr + PAGE_SIZE);
> @@ -172,7 +200,7 @@ static int __do_patch_instruction(u32 *addr, ppc_inst_t instr)
> return err;
> }
>
> -static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
> +static int __always_inline do_patch_memory(void *dest, unsigned long src, size_t size)
> {
> int err;
> unsigned long flags;
> @@ -183,32 +211,42 @@ static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
> * to allow patching. We just do the plain old patching
> */
> if (!static_branch_likely(&poking_init_done))
> - return raw_patch_instruction(addr, instr);
> + return ___patch_memory(dest, src, dest, size);
>
> local_irq_save(flags);
> - err = __do_patch_instruction(addr, instr);
> + err = __do_patch_memory(dest, src, size);
> local_irq_restore(flags);
>
> return err;
> }
> +
> #else /* !CONFIG_STRICT_KERNEL_RWX */
>
> -static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
> +static int do_patch_memory(void *dest, unsigned long src, size_t size)
> {
> - return raw_patch_instruction(addr, instr);
> + return ___patch_memory(dest, src, dest, size);
> }
>
> #endif /* CONFIG_STRICT_KERNEL_RWX */
>
> __ro_after_init DEFINE_STATIC_KEY_FALSE(init_mem_is_free);
>
> -int patch_instruction(u32 *addr, ppc_inst_t instr)
> +int __patch_memory(void *dest, unsigned long src, size_t size)
> {
> /* Make sure we aren't patching a freed init section */
> - if (static_branch_likely(&init_mem_is_free) && init_section_contains(addr, 4))
> + if (static_branch_likely(&init_mem_is_free) && init_section_contains(dest, 4))
> return 0;
>
> - return do_patch_instruction(addr, instr);
> + return do_patch_memory(dest, src, size);
> +}
> +NOKPROBE_SYMBOL(__patch_memory);
> +
> +int patch_instruction(u32 *addr, ppc_inst_t instr)
> +{
> + if (ppc_inst_prefixed(instr))
> + return patch_memory(addr, ppc_inst_as_ulong(instr));
> + else
> + return patch_memory(addr, ppc_inst_val(instr));
> }
> NOKPROBE_SYMBOL(patch_instruction);
>
> --
> 2.37.3
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