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SubjectRe: [PATCH v2 2/8] x86: return error code in text_poke_bp
On Fri,  8 Nov 2013 10:12:06 +0100
Petr Mladek <pmladek@suse.cz> wrote:

> We would like to use text_poke_bp in the dynamic ftrace which want to
> know about errors. For example, it informs about them in the ftrace log.
>
> Let's return the error code instead of the address. The address was just copied
> from the first parameter, so it was no extra information. The return value
> has not been used anywhere yet.
>
> There is a question whether we should recover the original opcode when
> the second or third text_poke_part fails in text_poke_bp. Well, the errors
> were ignored until now. It did not cause any real life problems. There is
> really small chance that the first byte (int3) can be written and the other
> parts of the code can not be modified. It is probably not worth the extra
> complexity.

I agree with Masami. If the first part succeeds, still check the other
parts, and if they don't succeed, then just do a BUG().


>
> Signed-off-by: Petr Mladek <pmladek@suse.cz>
> ---
> arch/x86/include/asm/alternative.h | 3 ++-
> arch/x86/kernel/alternative.c | 18 +++++++++++++-----
> 2 files changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
> index 0a3f9c9..f2343d8 100644
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -226,6 +226,7 @@ extern void *text_poke_early(void *addr, const void *opcode, size_t len);
> */
> extern void *text_poke(void *addr, const void *opcode, size_t len);
> extern int poke_int3_handler(struct pt_regs *regs);
> -extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
> +extern int text_poke_bp(void *addr, const void *opcode, size_t len,
> + void *handler);
>
> #endif /* _ASM_X86_ALTERNATIVE_H */
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 0586dc1..c459e62 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -673,9 +673,10 @@ int poke_int3_handler(struct pt_regs *regs)
> *
> * Note: must be called under text_mutex.
> */
> -void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
> +int text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
> {
> unsigned char int3 = 0xcc;
> + int ret;
>
> bp_int3_handler = handler;
> bp_int3_addr = (u8 *)addr + sizeof(int3);
> @@ -687,15 +688,19 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
> */
> smp_wmb();
>
> - text_poke_part(addr, &int3, sizeof(int3));
> + ret = text_poke_part(addr, &int3, sizeof(int3));
> + if (unlikely(ret))
> + goto fail;

Ah! you have it return an error code. May need to do that for all users
of text_poke_part().

-- Steve

>
> on_each_cpu(do_sync_core, NULL, 1);
>
> if (len - sizeof(int3) > 0) {
> /* patch all but the first byte */
> - text_poke_part((char *)addr + sizeof(int3),
> + ret = text_poke_part((char *)addr + sizeof(int3),
> (const char *) opcode + sizeof(int3),
> len - sizeof(int3));
> + if (unlikely(ret))
> + goto fail;
> /*
> * According to Intel, this core syncing is very likely
> * not necessary and we'd be safe even without it. But
> @@ -705,13 +710,16 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
> }
>
> /* patch the first byte */
> - text_poke_part(addr, opcode, sizeof(int3));
> + ret = text_poke_part(addr, opcode, sizeof(int3));
> + if (unlikely(ret))
> + goto fail;
>
> on_each_cpu(do_sync_core, NULL, 1);
>
> +fail:
> bp_patching_in_progress = false;
> smp_wmb();
>
> - return addr;
> + return ret;
> }
>



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