From: Dave Martin <Dave.Martin@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Jeremy Linton <jeremy.linton@arm.com>,
"H . J . Lu" <hjl.tools@gmail.com>,
Yu-cheng Yu <yu-cheng.yu@intel.com>,
linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
libc-alpha@sourceware.org
Subject: Re: [PATCH v2 2/3] arm64: Enable BTI for main executable as well as the interpreter
Date: Wed, 9 Jun 2021 16:17:13 +0100 [thread overview]
Message-ID: <20210609151713.GL4187@arm.com> (raw)
In-Reply-To: <20210604112450.13344-3-broonie@kernel.org>
On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote:
> Currently for dynamically linked ELF executables we only enable BTI for
> the interpreter, expecting the interpreter to do this for the main
> executable. This is a bit inconsistent since we do map main executable and
> is causing issues with systemd's MemoryDenyWriteExecute feature which is
> implemented using a seccomp filter which prevents setting PROT_EXEC on
> already mapped memory and lacks the context to be able to detect that
> memory is already mapped with PROT_EXEC.
>
> Resolve this by checking the BTI property for the main executable and
> enabling BTI if it is present when doing the initial mapping. This does
> mean that we may get more code with BTI enabled if running on a system
> without BTI support in the dynamic linker, this is expected to be a safe
> configuration and testing seems to confirm that. It also reduces the
> flexibility userspace has to disable BTI but it is expected that for cases
> where there are problems which require BTI to be disabled it is more likely
> that it will need to be disabled on a system level.
>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> Reviewed-by: Dave Martin <Dave.Martin@arm.com>
> ---
> arch/arm64/include/asm/elf.h | 14 ++++++++++----
> arch/arm64/kernel/process.c | 18 ++++++------------
> 2 files changed, 16 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> index a488a1329b16..9f86dbce2680 100644
> --- a/arch/arm64/include/asm/elf.h
> +++ b/arch/arm64/include/asm/elf.h
> @@ -253,7 +253,8 @@ struct arch_elf_state {
> int flags;
> };
>
> -#define ARM64_ELF_BTI (1 << 0)
> +#define ARM64_ELF_INTERP_BTI (1 << 0)
> +#define ARM64_ELF_EXEC_BTI (1 << 1)
>
> #define INIT_ARCH_ELF_STATE { \
> .flags = 0, \
> @@ -274,9 +275,14 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
> if (datasz != sizeof(*p))
> return -ENOEXEC;
>
> - if (system_supports_bti() && has_interp == is_interp &&
> - (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
> - arch->flags |= ARM64_ELF_BTI;
> + if (system_supports_bti() &&
> + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
> + if (is_interp) {
> + arch->flags |= ARM64_ELF_INTERP_BTI;
> + } else {
> + arch->flags |= ARM64_ELF_EXEC_BTI;
> + }
Nit: surplus curlies? (coding-style.rst does actually say to drop them
when all branches of an if are single-statement one-liners -- I had
presumed I was just being pedantic...)
> + }
> }
>
> return 0;
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index b4bb67f17a2c..f7fff4a4c99f 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -744,19 +744,13 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void)
> int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
> bool has_interp, bool is_interp)
> {
> - /*
> - * For dynamically linked executables the interpreter is
> - * responsible for setting PROT_BTI on everything except
> - * itself.
> - */
> - if (is_interp != has_interp)
> - return prot;
> + if (prot & PROT_EXEC) {
> + if (state->flags & ARM64_ELF_INTERP_BTI && is_interp)
> + prot |= PROT_BTI;
>
> - if (!(state->flags & ARM64_ELF_BTI))
> - return prot;
> -
> - if (prot & PROT_EXEC)
> - prot |= PROT_BTI;
> + if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp)
> + prot |= PROT_BTI;
> + }
Is it worth adding () around the bitwise-& expressions? I'm always a
little uneasy about the operator precedence of binary &, although
without looking it up I think you're correct.
Also, due to symmetry between arch_elf_adjust_prot() and
arch_parse_elf_properties() here, could we have something like
static inline int arm64_elf_bti_flag(bool is_interp)
{
if (is_interp)
return ARM64_ELF_INTERP_BTI;
else
return ARM64_ELF_EXEC_BTI;
}
and then have code like
if (state->flags & arm64_elf_bti_flag(is_interp))
prot |= PROT_BTI;
here (with analogous code in arch_elf_adjust_prot()).
Feel free to adopt if this appeals to you, otherwise I'm also fine with
your version.)
Either way, these comments are all pretty much cosmetic, and my
Reviewed-by stands.
Cheers
---Dave
next prev parent reply other threads:[~2021-06-09 15:18 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-04 11:24 [PATCH v2 0/3] arm64: Enable BTI for the executable as well as the interpreter Mark Brown
2021-06-04 11:24 ` [PATCH v2 1/3] elf: Allow architectures to parse properties on the main executable Mark Brown
2021-06-09 15:16 ` Dave Martin
2021-06-10 13:41 ` Mark Brown
2021-06-04 11:24 ` [PATCH v2 2/3] arm64: Enable BTI for main executable as well as the interpreter Mark Brown
2021-06-09 15:17 ` Dave Martin [this message]
2021-06-10 13:19 ` Mark Brown
2021-06-10 15:34 ` Dave Martin
2021-06-04 11:24 ` [PATCH v2 3/3] elf: Remove has_interp property from arch_adjust_elf_prot() Mark Brown
2021-06-09 15:17 ` Dave Martin
2021-06-09 16:55 ` Yu, Yu-cheng
2021-06-10 9:58 ` Dave Martin
2021-06-10 18:17 ` Yu, Yu-cheng
2021-06-10 13:34 ` Mark Brown
2021-06-10 15:40 ` Dave Martin
2021-06-10 16:28 ` [PATCH v2 0/3] arm64: Enable BTI for the executable as well as the interpreter Jeremy Linton
2021-06-14 16:00 ` Mark Brown
2021-06-15 15:22 ` Dave Martin
2021-06-15 15:33 ` Mark Brown
2021-06-15 15:41 ` Dave Martin
2021-06-16 5:12 ` Jeremy Linton
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210609151713.GL4187@arm.com \
--to=dave.martin@arm.com \
--cc=broonie@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=hjl.tools@gmail.com \
--cc=jeremy.linton@arm.com \
--cc=libc-alpha@sourceware.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=szabolcs.nagy@arm.com \
--cc=will@kernel.org \
--cc=yu-cheng.yu@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).