From: Eric W. Biederman <ebiederm@xmission.com>
Date: Tue, 4 May 2021 16:25:22 +0000 (-0500)
Subject: signal: Verify the alignment and size of siginfo_t
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=50ae81305c7a3ee802f0a1988503ce913c79cd6e;p=linux.git
signal: Verify the alignment and size of siginfo_t
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
Acked-by: Marco Elver <elver@google.com>
v1: https://lkml.kernel.org/r/20210505141101.11519-4-ebiederm@xmission.co
Link: https://lkml.kernel.org/r/875yxaxmyl.fsf_-_@disp2133
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 7ef453e8a96ff..f3800c0f428b7 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 4413b6a4e32a3..d3721e01441b0 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -1011,6 +1011,8 @@ 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/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index ab17752167125..d3be01c46becc 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 65fd26ae9d25f..4276b9e003ca5 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 a58e0cc45d24a..cea23cf956006 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 06743ec054d2a..b52407c56000e 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 5a3c221f4c9d3..3ba180f550d7c 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 {