From: dann frazier <dann.frazier@canonical.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: mark.rutland@arm.com, catalin.marinas@arm.com, duwe@lst.de,
will.deacon@arm.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64/module: ftrace: deal with place relative nature of PLTs
Date: Mon, 15 Apr 2019 12:47:05 -0600 [thread overview]
Message-ID: <20190415184705.GA21567@xps13.dannf> (raw)
In-Reply-To: <20190413065925.6981-1-ard.biesheuvel@linaro.org>
On Fri, Apr 12, 2019 at 11:59:25PM -0700, Ard Biesheuvel wrote:
> Another bodge for the ftrace PLT code: plt_entries_equal() now takes
> the place relative nature of the ADRP/ADD based PLT entries into
> account, which means that a struct trampoline instance on the stack
> is no longer equal to the same set of opcodes in the module struct,
> given that they don't point to the same place in memory anymore.
>
> Work around this by using memcmp() in the ftrace PLT handling code.
This fixes an issue I was seeing on a HiSilicon D06 server:
https://bugs.launchpad.net/bugs/1822871
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: dann frazier <dann.frazier@canonical.com>
-dann
> ---
> arch/arm64/kernel/ftrace.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index 07b298120182..65a51331088e 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -103,10 +103,15 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> * to be revisited if support for multiple ftrace entry points
> * is added in the future, but for now, the pr_err() below
> * deals with a theoretical issue only.
> + *
> + * Note that PLTs are place relative, and plt_entries_equal()
> + * checks whether they point to the same target. Here, we need
> + * to check if the actual opcodes are in fact identical,
> + * regardless of the offset in memory so use memcmp() instead.
> */
> trampoline = get_plt_entry(addr, mod->arch.ftrace_trampoline);
> - if (!plt_entries_equal(mod->arch.ftrace_trampoline,
> - &trampoline)) {
> + if (memcmp(mod->arch.ftrace_trampoline, &trampoline,
> + sizeof(trampoline))) {
> if (plt_entry_is_initialized(mod->arch.ftrace_trampoline)) {
> pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
> return -EINVAL;
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next prev parent reply other threads:[~2019-04-15 18:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-13 6:59 [PATCH] arm64/module: ftrace: deal with place relative nature of PLTs Ard Biesheuvel
2019-04-15 18:47 ` dann frazier [this message]
2019-04-23 11:43 ` Will Deacon
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