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From: Marco Elver <elver@google.com>
To: "Eric W. Beiderman" <ebiederm@xmission.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Florian Weimer <fweimer@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Collingbourne <pcc@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Alexander Potapenko <glider@google.com>,
	sparclinux <sparclinux@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH v3 04/12] signal: Verify the alignment and size of siginfo_t
Date: Wed, 5 May 2021 19:24:00 +0200
Message-ID: <CANpmjNNJ0vHq3s+mEqR1q8jqCzgHmivRcU+1m_Q8vquV5t5xWw@mail.gmail.com> (raw)
In-Reply-To: <20210505141101.11519-4-ebiederm@xmission.com>

On Wed, 5 May 2021 at 16:11, Eric W. Beiderman <ebiederm@xmission.com> wrote:
> From: "Eric W. Biederman" <ebiederm@xmission.com>
>
> Update the static assertions about siginfo_t to also describe
> it's alignment and size.
>
> While investigating if it was possible to add a 64bit field into
> siginfo_t[1] it became apparent that the alignment of siginfo_t
> is as much a part of the ABI as the size of the structure.
>
> If the alignment changes siginfo_t when embedded in another structure
> can move to a different offset.  Which is not acceptable from an ABI
> structure.
>
> So document that fact and add static assertions to notify developers
> if they change change the alignment by accident.
>
> [1] https://lkml.kernel.org/r/YJEZdhe6JGFNYlum@elver.google.com
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

Acked-by: Marco Elver <elver@google.com>

> ---
>  arch/arm/kernel/signal.c           | 2 ++
>  arch/arm64/kernel/signal.c         | 2 ++
>  arch/arm64/kernel/signal32.c       | 2 ++
>  arch/sparc/kernel/signal32.c       | 2 ++
>  arch/sparc/kernel/signal_64.c      | 2 ++
>  arch/x86/kernel/signal_compat.c    | 6 ++++++
>  include/uapi/asm-generic/siginfo.h | 5 +++++
>  7 files changed, 21 insertions(+)
>
> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
> index 2dac5d2c5cf6..643bcb0f091b 100644
> --- a/arch/arm/kernel/signal.c
> +++ b/arch/arm/kernel/signal.c
> @@ -737,6 +737,8 @@ static_assert(NSIGBUS       == 5);
>  static_assert(NSIGTRAP == 6);
>  static_assert(NSIGCHLD == 6);
>  static_assert(NSIGSYS  == 2);
> +static_assert(sizeof(siginfo_t) == 128);
> +static_assert(__alignof__(siginfo_t) == 4);
>  static_assert(offsetof(siginfo_t, si_signo)    == 0x00);
>  static_assert(offsetof(siginfo_t, si_errno)    == 0x04);
>  static_assert(offsetof(siginfo_t, si_code)     == 0x08);
> diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
> index af8bd2af1298..ad4bd27fc044 100644
> --- a/arch/arm64/kernel/signal.c
> +++ b/arch/arm64/kernel/signal.c
> @@ -985,6 +985,8 @@ static_assert(NSIGBUS       == 5);
>  static_assert(NSIGTRAP == 6);
>  static_assert(NSIGCHLD == 6);
>  static_assert(NSIGSYS  == 2);
> +static_assert(sizeof(siginfo_t) == 128);

Would using SI_MAX_SIZE be appropriate? Perhaps not.. in case somebody
changes it, given these static asserts are meant to double-check.

I leave it to you to decide what makes more sense.

> +static_assert(__alignof__(siginfo_t) == 8);
>  static_assert(offsetof(siginfo_t, si_signo)    == 0x00);
>  static_assert(offsetof(siginfo_t, si_errno)    == 0x04);
>  static_assert(offsetof(siginfo_t, si_code)     == 0x08);
> diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
> index b6afb646515f..ee6c7484e130 100644
> --- a/arch/arm64/kernel/signal32.c
> +++ b/arch/arm64/kernel/signal32.c
> @@ -469,6 +469,8 @@ static_assert(NSIGBUS       == 5);
>  static_assert(NSIGTRAP == 6);
>  static_assert(NSIGCHLD == 6);
>  static_assert(NSIGSYS  == 2);
> +static_assert(sizeof(compat_siginfo_t) == 128);
> +static_assert(__alignof__(compat_siginfo_t) == 4);
>  static_assert(offsetof(compat_siginfo_t, si_signo)     == 0x00);
>  static_assert(offsetof(compat_siginfo_t, si_errno)     == 0x04);
>  static_assert(offsetof(compat_siginfo_t, si_code)      == 0x08);
> diff --git a/arch/sparc/kernel/signal32.c b/arch/sparc/kernel/signal32.c
> index 778ed5c26d4a..32b977f253e3 100644
> --- a/arch/sparc/kernel/signal32.c
> +++ b/arch/sparc/kernel/signal32.c
> @@ -757,6 +757,8 @@ static_assert(NSIGBUS       == 5);
>  static_assert(NSIGTRAP == 6);
>  static_assert(NSIGCHLD == 6);
>  static_assert(NSIGSYS  == 2);
> +static_assert(sizeof(compat_siginfo_t) == 128);
> +static_assert(__alignof__(compat_siginfo_t) == 4);
>  static_assert(offsetof(compat_siginfo_t, si_signo)     == 0x00);
>  static_assert(offsetof(compat_siginfo_t, si_errno)     == 0x04);
>  static_assert(offsetof(compat_siginfo_t, si_code)      == 0x08);
> diff --git a/arch/sparc/kernel/signal_64.c b/arch/sparc/kernel/signal_64.c
> index c9bbf5f29078..e9dda9db156c 100644
> --- a/arch/sparc/kernel/signal_64.c
> +++ b/arch/sparc/kernel/signal_64.c
> @@ -567,6 +567,8 @@ static_assert(NSIGBUS       == 5);
>  static_assert(NSIGTRAP == 6);
>  static_assert(NSIGCHLD == 6);
>  static_assert(NSIGSYS  == 2);
> +static_assert(sizeof(siginfo_t) == 128);
> +static_assert(__alignof__(siginfo_t) == 8);
>  static_assert(offsetof(siginfo_t, si_signo)    == 0x00);
>  static_assert(offsetof(siginfo_t, si_errno)    == 0x04);
>  static_assert(offsetof(siginfo_t, si_code)     == 0x08);
> diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
> index 0e5d0a7e203b..e735bc129331 100644
> --- a/arch/x86/kernel/signal_compat.c
> +++ b/arch/x86/kernel/signal_compat.c
> @@ -34,7 +34,13 @@ static inline void signal_compat_build_tests(void)
>         BUILD_BUG_ON(NSIGSYS  != 2);
>
>         /* This is part of the ABI and can never change in size: */
> +       BUILD_BUG_ON(sizeof(siginfo_t) != 128);
>         BUILD_BUG_ON(sizeof(compat_siginfo_t) != 128);
> +
> +       /* This is a part of the ABI and can never change in alignment */
> +       BUILD_BUG_ON(__alignof__(siginfo_t) != 8);
> +       BUILD_BUG_ON(__alignof__(compat_siginfo_t) != 4);
> +
>         /*
>          * The offsets of all the (unioned) si_fields are fixed
>          * in the ABI, of course.  Make sure none of them ever
> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index 03d6f6d2c1fe..91c80d0c10c5 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -29,6 +29,11 @@ typedef union sigval {
>  #define __ARCH_SI_ATTRIBUTES
>  #endif
>
> +/*
> + * Be careful when extending this union.  On 32bit siginfo_t is 32bit
> + * aligned.  Which means that a 64bit field or any other field that
> + * would increase the alignment of siginfo_t will break the ABI.
> + */
>  union __sifields {
>         /* kill() */
>         struct {
> --
> 2.30.1
>

  reply index

Thread overview: 103+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-29  7:48 siginfo_t ABI break on sparc64 from si_addr_lsb move 3y ago Marco Elver
2021-04-29 17:23 ` Eric W. Biederman
2021-04-29 18:46   ` Marco Elver
2021-04-29 20:48   ` Arnd Bergmann
2021-04-30 17:08     ` Eric W. Biederman
2021-04-30 19:07       ` Marco Elver
2021-04-30 20:15         ` Eric W. Biederman
2021-04-30 23:50           ` Marco Elver
2021-04-30 22:49         ` [RFC][PATCH 0/3] signal: Move si_trapno into the _si_fault union Eric W. Biederman
2021-04-30 22:50           ` [PATCH 1/3] siginfo: Move si_trapno inside the union inside _si_fault Eric W. Biederman
2021-05-01 10:31             ` Marco Elver
2021-05-02 18:27               ` Eric W. Biederman
2021-04-30 22:54           ` [PATCH 2/3] signal: Implement SIL_FAULT_TRAPNO Eric W. Biederman
2021-04-30 23:19             ` Eric W. Biederman
2021-05-01 10:33             ` Marco Elver
2021-05-02 18:24               ` Eric W. Biederman
2021-04-30 22:55           ` [PATCH 3/3] signal: Use dedicated helpers to send signals with si_trapno set Eric W. Biederman
2021-05-01 10:33             ` Marco Elver
2021-04-30 22:56           ` [PATCH 4/3] signal: Remove __ARCH_SI_TRAPNO Eric W. Biederman
2021-04-30 23:23           ` Is perf_sigtrap synchronous? Eric W. Biederman
2021-05-01  0:28             ` Marco Elver
2021-04-30 23:42           ` [PATCH 5/3] signal: Rename SIL_PERF_EVENT SIL_FAULT_PERF_EVENT for consistency Eric W. Biederman
2021-05-01 10:35             ` Marco Elver
2021-04-30 23:43           ` [PATCH 6/3] signal: Factor force_sig_perf out of perf_sigtrap Eric W. Biederman
2021-05-01 10:45             ` Marco Elver
2021-04-30 23:43           ` [PATCH 7/3] signal: Deliver all of the perf_data in si_perf Eric W. Biederman
2021-05-01 10:47             ` Marco Elver
2021-05-02 18:39               ` Eric W. Biederman
2021-05-02 19:13                 ` Marco Elver
2021-05-03 12:44                 ` Peter Zijlstra
2021-05-03 19:38                   ` Eric W. Biederman
2021-05-03 19:53                     ` Marco Elver
2021-04-30 23:47           ` [RFC][PATCH 0/3] signal: Move si_trapno into the _si_fault union Eric W. Biederman
2021-05-01  0:37             ` Marco Elver
2021-05-01 15:16               ` Eric W. Biederman
2021-05-01 16:24                 ` Marco Elver
2021-05-03 20:25                   ` [PATCH 00/12] signal: sort out si_trapno and si_perf Eric W. Biederman
2021-05-03 20:38                     ` [PATCH 01/12] sparc64: Add compile-time asserts for siginfo_t offsets Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 02/12] arm: " Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 03/12] arm64: " Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 04/12] siginfo: Move si_trapno inside the union inside _si_fault Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 05/12] signal: Implement SIL_FAULT_TRAPNO Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 06/12] signal: Use dedicated helpers to send signals with si_trapno set Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 07/12] signal: Remove __ARCH_SI_TRAPNO Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 08/12] signal: Rename SIL_PERF_EVENT SIL_FAULT_PERF_EVENT for consistency Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 09/12] signal: Factor force_sig_perf out of perf_sigtrap Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 10/12] signal: Redefine signinfo so 64bit fields are possible Eric W. Beiderman
2021-05-03 21:04                         ` Eric W. Biederman
2021-05-03 22:47                           ` Marco Elver
2021-05-04  3:42                             ` Eric W. Biederman
2021-05-04  4:03                               ` Peter Collingbourne
2021-05-04  9:52                                 ` Marco Elver
2021-05-04 16:16                                   ` Eric W. Biederman
2021-05-03 20:38                       ` [PATCH 11/12] signal: Deliver all of the siginfo perf data in _perf Eric W. Beiderman
2021-05-03 20:38                       ` [PATCH 12/12] signalfd: Remove SIL_FAULT_PERF_EVENT fields from signalfd_siginfo Eric W. Beiderman
2021-05-04 21:13                     ` [PATCH v3 00/12] signal: sort out si_trapno and si_perf Eric W. Biederman
2021-05-04 22:05                       ` Marco Elver
2021-05-05 14:12                         ` Eric W. Biederman
2021-05-05 14:10                       ` [PATCH v3 01/12] sparc64: Add compile-time asserts for siginfo_t offsets Eric W. Beiderman
2021-05-05 14:10                         ` [PATCH v3 02/12] arm: " Eric W. Beiderman
2021-05-05 14:10                         ` [PATCH v3 03/12] arm64: " Eric W. Beiderman
2021-05-05 14:10                         ` [PATCH v3 04/12] signal: Verify the alignment and size of siginfo_t Eric W. Beiderman
2021-05-05 17:24                           ` Marco Elver [this message]
2021-05-05 14:10                         ` [PATCH v3 05/12] siginfo: Move si_trapno inside the union inside _si_fault Eric W. Beiderman
2021-05-05 14:10                         ` [PATCH v3 06/12] signal: Implement SIL_FAULT_TRAPNO Eric W. Beiderman
2021-05-05 17:25                           ` Marco Elver
2021-05-05 14:10                         ` [PATCH v3 07/12] signal: Use dedicated helpers to send signals with si_trapno set Eric W. Beiderman
2021-05-05 17:25                           ` Marco Elver
2021-05-05 14:10                         ` [PATCH v3 08/12] signal: Remove __ARCH_SI_TRAPNO Eric W. Beiderman
2021-05-05 17:25                           ` Marco Elver
2021-05-05 14:10                         ` [PATCH v3 09/12] signal: Rename SIL_PERF_EVENT SIL_FAULT_PERF_EVENT for consistency Eric W. Beiderman
2021-05-05 17:26                           ` Marco Elver
2021-05-05 14:10                         ` [PATCH v3 10/12] signal: Factor force_sig_perf out of perf_sigtrap Eric W. Beiderman
2021-05-05 17:26                           ` Marco Elver
2021-05-06 10:54                           ` Peter Zijlstra
2021-05-05 14:11                         ` [PATCH v3 11/12] signal: Deliver all of the siginfo perf data in _perf Eric W. Beiderman
2021-05-05 17:27                           ` Marco Elver
2021-05-05 14:11                         ` [PATCH v3 12/12] signalfd: Remove SIL_FAULT_PERF_EVENT fields from signalfd_siginfo Eric W. Beiderman
2021-05-05 17:27                           ` Marco Elver
2021-05-05 17:28                       ` [PATCH v3 00/12] signal: sort out si_trapno and si_perf Marco Elver
2021-05-06  7:00                       ` Geert Uytterhoeven
2021-05-06 10:43                         ` Marco Elver
2021-05-06 15:28                           ` Eric W. Biederman
2021-05-06 15:14                         ` Eric W. Biederman
2021-05-14  4:54                       ` [GIT PULL] siginfo: ABI fixes for v5.13-rc2 Eric W. Biederman
2021-05-14 19:14                         ` Linus Torvalds
2021-05-14 21:15                           ` Eric W. Biederman
2021-05-14 22:38                             ` Eric W. Biederman
2021-05-16  7:40                         ` Ingo Molnar
2021-05-17 15:29                           ` Eric W. Biederman
2021-05-21 14:59                         ` [GIT PULL] siginfo: ABI fixes for v5.13-rc3 Eric W. Biederman
2021-05-21 16:34                           ` pr-tracker-bot
2021-05-17 19:56                       ` [PATCH v4 0/5] siginfo: ABI fixes for TRAP_PERF Eric W. Biederman
2021-05-17 19:57                         ` [PATCH v4 1/5] siginfo: Move si_trapno inside the union inside _si_fault Eric W. Beiderman
2021-05-17 19:57                           ` [PATCH v4 2/5] signal: Implement SIL_FAULT_TRAPNO Eric W. Beiderman
2021-05-17 19:57                           ` [PATCH v4 3/5] signal: Factor force_sig_perf out of perf_sigtrap Eric W. Beiderman
2021-05-17 19:57                           ` [PATCH v4 4/5] signal: Deliver all of the siginfo perf data in _perf Eric W. Beiderman
2021-05-17 19:57                           ` [PATCH v4 5/5] signalfd: Remove SIL_PERF_EVENT fields from signalfd_siginfo Eric W. Beiderman
2021-05-17 20:53                         ` [PATCH v4 0/5] siginfo: ABI fixes for TRAP_PERF Marco Elver
2021-05-18  3:46                           ` Eric W. Biederman
2021-05-18  6:44                             ` Marco Elver
2021-05-01 16:26               ` [RFC][PATCH 0/3] signal: Move si_trapno into the _si_fault union Marco Elver
2021-04-30 20:43       ` siginfo_t ABI break on sparc64 from si_addr_lsb move 3y ago Arnd Bergmann

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