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linux/arch/x86/kernel/signal_compat.c
Eric W. Biederman 50ae81305c 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>
2021-07-23 13:15:31 -05:00

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// SPDX-License-Identifier: GPL-2.0
#include <linux/compat.h>
#include <linux/uaccess.h>
#include <linux/ptrace.h>
/*
* The compat_siginfo_t structure and handing code is very easy
* to break in several ways. It must always be updated when new
* updates are made to the main siginfo_t, and
* copy_siginfo_to_user32() must be updated when the
* (arch-independent) copy_siginfo_to_user() is updated.
*
* It is also easy to put a new member in the compat_siginfo_t
* which has implicit alignment which can move internal structure
* alignment around breaking the ABI. This can happen if you,
* for instance, put a plain 64-bit value in there.
*/
static inline void signal_compat_build_tests(void)
{
int _sifields_offset = offsetof(compat_siginfo_t, _sifields);
/*
* If adding a new si_code, there is probably new data in
* the siginfo. Make sure folks bumping the si_code
* limits also have to look at this code. Make sure any
* new fields are handled in copy_siginfo_to_user32()!
*/
BUILD_BUG_ON(NSIGILL != 11);
BUILD_BUG_ON(NSIGFPE != 15);
BUILD_BUG_ON(NSIGSEGV != 9);
BUILD_BUG_ON(NSIGBUS != 5);
BUILD_BUG_ON(NSIGTRAP != 6);
BUILD_BUG_ON(NSIGCHLD != 6);
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
* move and are always at the beginning:
*/
BUILD_BUG_ON(offsetof(compat_siginfo_t, _sifields) != 3 * sizeof(int));
#define CHECK_CSI_OFFSET(name) BUILD_BUG_ON(_sifields_offset != offsetof(compat_siginfo_t, _sifields.name))
BUILD_BUG_ON(offsetof(siginfo_t, si_signo) != 0);
BUILD_BUG_ON(offsetof(siginfo_t, si_errno) != 4);
BUILD_BUG_ON(offsetof(siginfo_t, si_code) != 8);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_signo) != 0);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_errno) != 4);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_code) != 8);
/*
* Ensure that the size of each si_field never changes.
* If it does, it is a sign that the
* copy_siginfo_to_user32() code below needs to updated
* along with the size in the CHECK_SI_SIZE().
*
* We repeat this check for both the generic and compat
* siginfos.
*
* Note: it is OK for these to grow as long as the whole
* structure stays within the padding size (checked
* above).
*/
#define CHECK_CSI_SIZE(name, size) BUILD_BUG_ON(size != sizeof(((compat_siginfo_t *)0)->_sifields.name))
#define CHECK_SI_SIZE(name, size) BUILD_BUG_ON(size != sizeof(((siginfo_t *)0)->_sifields.name))
CHECK_CSI_OFFSET(_kill);
CHECK_CSI_SIZE (_kill, 2*sizeof(int));
CHECK_SI_SIZE (_kill, 2*sizeof(int));
BUILD_BUG_ON(offsetof(siginfo_t, si_pid) != 0x10);
BUILD_BUG_ON(offsetof(siginfo_t, si_uid) != 0x14);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_pid) != 0xC);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_uid) != 0x10);
CHECK_CSI_OFFSET(_timer);
CHECK_CSI_SIZE (_timer, 3*sizeof(int));
CHECK_SI_SIZE (_timer, 6*sizeof(int));
BUILD_BUG_ON(offsetof(siginfo_t, si_tid) != 0x10);
BUILD_BUG_ON(offsetof(siginfo_t, si_overrun) != 0x14);
BUILD_BUG_ON(offsetof(siginfo_t, si_value) != 0x18);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_tid) != 0x0C);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_overrun) != 0x10);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_value) != 0x14);
CHECK_CSI_OFFSET(_rt);
CHECK_CSI_SIZE (_rt, 3*sizeof(int));
CHECK_SI_SIZE (_rt, 4*sizeof(int));
BUILD_BUG_ON(offsetof(siginfo_t, si_pid) != 0x10);
BUILD_BUG_ON(offsetof(siginfo_t, si_uid) != 0x14);
BUILD_BUG_ON(offsetof(siginfo_t, si_value) != 0x18);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_pid) != 0x0C);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_uid) != 0x10);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_value) != 0x14);
CHECK_CSI_OFFSET(_sigchld);
CHECK_CSI_SIZE (_sigchld, 5*sizeof(int));
CHECK_SI_SIZE (_sigchld, 8*sizeof(int));
BUILD_BUG_ON(offsetof(siginfo_t, si_pid) != 0x10);
BUILD_BUG_ON(offsetof(siginfo_t, si_uid) != 0x14);
BUILD_BUG_ON(offsetof(siginfo_t, si_status) != 0x18);
BUILD_BUG_ON(offsetof(siginfo_t, si_utime) != 0x20);
BUILD_BUG_ON(offsetof(siginfo_t, si_stime) != 0x28);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_pid) != 0x0C);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_uid) != 0x10);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_status) != 0x14);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_utime) != 0x18);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_stime) != 0x1C);
#ifdef CONFIG_X86_X32_ABI
CHECK_CSI_OFFSET(_sigchld_x32);
CHECK_CSI_SIZE (_sigchld_x32, 7*sizeof(int));
/* no _sigchld_x32 in the generic siginfo_t */
BUILD_BUG_ON(offsetof(compat_siginfo_t, _sifields._sigchld_x32._utime) != 0x18);
BUILD_BUG_ON(offsetof(compat_siginfo_t, _sifields._sigchld_x32._stime) != 0x20);
#endif
CHECK_CSI_OFFSET(_sigfault);
CHECK_CSI_SIZE (_sigfault, 4*sizeof(int));
CHECK_SI_SIZE (_sigfault, 8*sizeof(int));
BUILD_BUG_ON(offsetof(siginfo_t, si_addr) != 0x10);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr) != 0x0C);
BUILD_BUG_ON(offsetof(siginfo_t, si_trapno) != 0x18);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_trapno) != 0x10);
BUILD_BUG_ON(offsetof(siginfo_t, si_addr_lsb) != 0x18);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_addr_lsb) != 0x10);
BUILD_BUG_ON(offsetof(siginfo_t, si_lower) != 0x20);
BUILD_BUG_ON(offsetof(siginfo_t, si_upper) != 0x28);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_lower) != 0x14);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_upper) != 0x18);
BUILD_BUG_ON(offsetof(siginfo_t, si_pkey) != 0x20);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_pkey) != 0x14);
BUILD_BUG_ON(offsetof(siginfo_t, si_perf_data) != 0x18);
BUILD_BUG_ON(offsetof(siginfo_t, si_perf_type) != 0x20);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_perf_data) != 0x10);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_perf_type) != 0x14);
CHECK_CSI_OFFSET(_sigpoll);
CHECK_CSI_SIZE (_sigpoll, 2*sizeof(int));
CHECK_SI_SIZE (_sigpoll, 4*sizeof(int));
BUILD_BUG_ON(offsetof(siginfo_t, si_band) != 0x10);
BUILD_BUG_ON(offsetof(siginfo_t, si_fd) != 0x18);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_band) != 0x0C);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_fd) != 0x10);
CHECK_CSI_OFFSET(_sigsys);
CHECK_CSI_SIZE (_sigsys, 3*sizeof(int));
CHECK_SI_SIZE (_sigsys, 4*sizeof(int));
BUILD_BUG_ON(offsetof(siginfo_t, si_call_addr) != 0x10);
BUILD_BUG_ON(offsetof(siginfo_t, si_syscall) != 0x18);
BUILD_BUG_ON(offsetof(siginfo_t, si_arch) != 0x1C);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_call_addr) != 0x0C);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_syscall) != 0x10);
BUILD_BUG_ON(offsetof(compat_siginfo_t, si_arch) != 0x14);
/* any new si_fields should be added here */
}
void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact)
{
signal_compat_build_tests();
if (!act)
return;
if (in_ia32_syscall())
act->sa.sa_flags |= SA_IA32_ABI;
if (in_x32_syscall())
act->sa.sa_flags |= SA_X32_ABI;
}
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