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linux/arch/x86/kernel/signal_32.c
Rick Edgecombe a5f6c2ace9 x86/shstk: Add user control-protection fault handler 
A control-protection fault is triggered when a control-flow transfer
attempt violates Shadow Stack or Indirect Branch Tracking constraints.
For example, the return address for a RET instruction differs from the copy
on the shadow stack.

There already exists a control-protection fault handler for handling kernel
IBT faults. Refactor this fault handler into separate user and kernel
handlers, like the page fault handler. Add a control-protection handler
for usermode. To avoid ifdeffery, put them both in a new file cet.c, which
is compiled in the case of either of the two CET features supported in the
kernel: kernel IBT or user mode shadow stack. Move some static inline
functions from traps.c into a header so they can be used in cet.c.

Opportunistically fix a comment in the kernel IBT part of the fault
handler that is on the end of the line instead of preceding it.

Keep the same behavior for the kernel side of the fault handler, except for
converting a BUG to a WARN in the case of a #CP happening when the feature
is missing. This unifies the behavior with the new shadow stack code, and
also prevents the kernel from crashing under this situation which is
potentially recoverable.

The control-protection fault handler works in a similar way as the general
protection fault handler. It provides the si_code SEGV_CPERR to the signal
handler.

Co-developed-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/all/20230613001108.3040476-28-rick.p.edgecombe%40intel.com
2023-08-02 15:01:50 -07:00

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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 1991, 1992 Linus Torvalds
*
* 1997-11-28 Modified for POSIX.1b signals by Richard Henderson
* 2000-06-20 Pentium III FXSR, SSE support by Gareth Hughes
* 2000-12-* x86-64 compatibility mode signal handling by Andi Kleen
*/
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/wait.h>
#include <linux/unistd.h>
#include <linux/stddef.h>
#include <linux/personality.h>
#include <linux/compat.h>
#include <linux/binfmts.h>
#include <linux/syscalls.h>
#include <asm/ucontext.h>
#include <linux/uaccess.h>
#include <asm/fpu/signal.h>
#include <asm/ptrace.h>
#include <asm/user32.h>
#include <uapi/asm/sigcontext.h>
#include <asm/proto.h>
#include <asm/vdso.h>
#include <asm/sigframe.h>
#include <asm/sighandling.h>
#include <asm/smap.h>
#include <asm/gsseg.h>
#ifdef CONFIG_IA32_EMULATION
#include <asm/ia32_unistd.h>
static inline void reload_segments(struct sigcontext_32 *sc)
{
unsigned int cur;
savesegment(gs, cur);
if ((sc->gs | 0x03) != cur)
load_gs_index(sc->gs | 0x03);
savesegment(fs, cur);
if ((sc->fs | 0x03) != cur)
loadsegment(fs, sc->fs | 0x03);
savesegment(ds, cur);
if ((sc->ds | 0x03) != cur)
loadsegment(ds, sc->ds | 0x03);
savesegment(es, cur);
if ((sc->es | 0x03) != cur)
loadsegment(es, sc->es | 0x03);
}
#define sigset32_t compat_sigset_t
#define siginfo32_t compat_siginfo_t
#define restore_altstack32 compat_restore_altstack
#define unsafe_save_altstack32 unsafe_compat_save_altstack
#else
#define sigset32_t sigset_t
#define siginfo32_t siginfo_t
#define __NR_ia32_sigreturn __NR_sigreturn
#define __NR_ia32_rt_sigreturn __NR_rt_sigreturn
#define restore_altstack32 restore_altstack
#define unsafe_save_altstack32 unsafe_save_altstack
#define __copy_siginfo_to_user32 copy_siginfo_to_user
#endif
/*
* Do a signal return; undo the signal stack.
*/
static bool ia32_restore_sigcontext(struct pt_regs *regs,
struct sigcontext_32 __user *usc)
{
struct sigcontext_32 sc;
/* Always make any pending restarted system calls return -EINTR */
current->restart_block.fn = do_no_restart_syscall;
if (unlikely(copy_from_user(&sc, usc, sizeof(sc))))
return false;
/* Get only the ia32 registers. */
regs->bx = sc.bx;
regs->cx = sc.cx;
regs->dx = sc.dx;
regs->si = sc.si;
regs->di = sc.di;
regs->bp = sc.bp;
regs->ax = sc.ax;
regs->sp = sc.sp;
regs->ip = sc.ip;
/* Get CS/SS and force CPL3 */
regs->cs = sc.cs | 0x03;
regs->ss = sc.ss | 0x03;
regs->flags = (regs->flags & ~FIX_EFLAGS) | (sc.flags & FIX_EFLAGS);
/* disable syscall checks */
regs->orig_ax = -1;
#ifdef CONFIG_IA32_EMULATION
/*
* Reload fs and gs if they have changed in the signal
* handler. This does not handle long fs/gs base changes in
* the handler, but does not clobber them at least in the
* normal case.
*/
reload_segments(&sc);
#else
loadsegment(gs, sc.gs);
regs->fs = sc.fs;
regs->es = sc.es;
regs->ds = sc.ds;
#endif
return fpu__restore_sig(compat_ptr(sc.fpstate), 1);
}
SYSCALL32_DEFINE0(sigreturn)
{
struct pt_regs *regs = current_pt_regs();
struct sigframe_ia32 __user *frame = (struct sigframe_ia32 __user *)(regs->sp-8);
sigset_t set;
if (!access_ok(frame, sizeof(*frame)))
goto badframe;
if (__get_user(set.sig[0], &frame->sc.oldmask)
|| __get_user(((__u32 *)&set)[1], &frame->extramask[0]))
goto badframe;
set_current_blocked(&set);
if (!ia32_restore_sigcontext(regs, &frame->sc))
goto badframe;
return regs->ax;
badframe:
signal_fault(regs, frame, "32bit sigreturn");
return 0;
}
SYSCALL32_DEFINE0(rt_sigreturn)
{
struct pt_regs *regs = current_pt_regs();
struct rt_sigframe_ia32 __user *frame;
sigset_t set;
frame = (struct rt_sigframe_ia32 __user *)(regs->sp - 4);
if (!access_ok(frame, sizeof(*frame)))
goto badframe;
if (__get_user(*(__u64 *)&set, (__u64 __user *)&frame->uc.uc_sigmask))
goto badframe;
set_current_blocked(&set);
if (!ia32_restore_sigcontext(regs, &frame->uc.uc_mcontext))
goto badframe;
if (restore_altstack32(&frame->uc.uc_stack))
goto badframe;
return regs->ax;
badframe:
signal_fault(regs, frame, "32bit rt sigreturn");
return 0;
}
/*
* Set up a signal frame.
*/
#define get_user_seg(seg) ({ unsigned int v; savesegment(seg, v); v; })
static __always_inline int
__unsafe_setup_sigcontext32(struct sigcontext_32 __user *sc,
void __user *fpstate,
struct pt_regs *regs, unsigned int mask)
{
unsafe_put_user(get_user_seg(gs), (unsigned int __user *)&sc->gs, Efault);
#ifdef CONFIG_IA32_EMULATION
unsafe_put_user(get_user_seg(fs), (unsigned int __user *)&sc->fs, Efault);
unsafe_put_user(get_user_seg(ds), (unsigned int __user *)&sc->ds, Efault);
unsafe_put_user(get_user_seg(es), (unsigned int __user *)&sc->es, Efault);
#else
unsafe_put_user(regs->fs, (unsigned int __user *)&sc->fs, Efault);
unsafe_put_user(regs->es, (unsigned int __user *)&sc->es, Efault);
unsafe_put_user(regs->ds, (unsigned int __user *)&sc->ds, Efault);
#endif
unsafe_put_user(regs->di, &sc->di, Efault);
unsafe_put_user(regs->si, &sc->si, Efault);
unsafe_put_user(regs->bp, &sc->bp, Efault);
unsafe_put_user(regs->sp, &sc->sp, Efault);
unsafe_put_user(regs->bx, &sc->bx, Efault);
unsafe_put_user(regs->dx, &sc->dx, Efault);
unsafe_put_user(regs->cx, &sc->cx, Efault);
unsafe_put_user(regs->ax, &sc->ax, Efault);
unsafe_put_user(current->thread.trap_nr, &sc->trapno, Efault);
unsafe_put_user(current->thread.error_code, &sc->err, Efault);
unsafe_put_user(regs->ip, &sc->ip, Efault);
unsafe_put_user(regs->cs, (unsigned int __user *)&sc->cs, Efault);
unsafe_put_user(regs->flags, &sc->flags, Efault);
unsafe_put_user(regs->sp, &sc->sp_at_signal, Efault);
unsafe_put_user(regs->ss, (unsigned int __user *)&sc->ss, Efault);
unsafe_put_user(ptr_to_compat(fpstate), &sc->fpstate, Efault);
/* non-iBCS2 extensions.. */
unsafe_put_user(mask, &sc->oldmask, Efault);
unsafe_put_user(current->thread.cr2, &sc->cr2, Efault);
return 0;
Efault:
return -EFAULT;
}
#define unsafe_put_sigcontext32(sc, fp, regs, set, label) \
do { \
if (__unsafe_setup_sigcontext32(sc, fp, regs, set->sig[0])) \
goto label; \
} while(0)
int ia32_setup_frame(struct ksignal *ksig, struct pt_regs *regs)
{
sigset32_t *set = (sigset32_t *) sigmask_to_save();
struct sigframe_ia32 __user *frame;
void __user *restorer;
void __user *fp = NULL;
/* copy_to_user optimizes that into a single 8 byte store */
static const struct {
u16 poplmovl;
u32 val;
u16 int80;
} __attribute__((packed)) code = {
0xb858, /* popl %eax ; movl $...,%eax */
__NR_ia32_sigreturn,
0x80cd, /* int $0x80 */
};
frame = get_sigframe(ksig, regs, sizeof(*frame), &fp);
if (ksig->ka.sa.sa_flags & SA_RESTORER) {
restorer = ksig->ka.sa.sa_restorer;
} else {
/* Return stub is in 32bit vsyscall page */
if (current->mm->context.vdso)
restorer = current->mm->context.vdso +
vdso_image_32.sym___kernel_sigreturn;
else
restorer = &frame->retcode;
}
if (!user_access_begin(frame, sizeof(*frame)))
return -EFAULT;
unsafe_put_user(ksig->sig, &frame->sig, Efault);
unsafe_put_sigcontext32(&frame->sc, fp, regs, set, Efault);
unsafe_put_user(set->sig[1], &frame->extramask[0], Efault);
unsafe_put_user(ptr_to_compat(restorer), &frame->pretcode, Efault);
/*
* These are actually not used anymore, but left because some
* gdb versions depend on them as a marker.
*/
unsafe_put_user(*((u64 *)&code), (u64 __user *)frame->retcode, Efault);
user_access_end();
/* Set up registers for signal handler */
regs->sp = (unsigned long) frame;
regs->ip = (unsigned long) ksig->ka.sa.sa_handler;
/* Make -mregparm=3 work */
regs->ax = ksig->sig;
regs->dx = 0;
regs->cx = 0;
#ifdef CONFIG_IA32_EMULATION
loadsegment(ds, __USER_DS);
loadsegment(es, __USER_DS);
#else
regs->ds = __USER_DS;
regs->es = __USER_DS;
#endif
regs->cs = __USER32_CS;
regs->ss = __USER_DS;
return 0;
Efault:
user_access_end();
return -EFAULT;
}
int ia32_setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
{
sigset32_t *set = (sigset32_t *) sigmask_to_save();
struct rt_sigframe_ia32 __user *frame;
void __user *restorer;
void __user *fp = NULL;
/* unsafe_put_user optimizes that into a single 8 byte store */
static const struct {
u8 movl;
u32 val;
u16 int80;
u8 pad;
} __attribute__((packed)) code = {
0xb8,
__NR_ia32_rt_sigreturn,
0x80cd,
0,
};
frame = get_sigframe(ksig, regs, sizeof(*frame), &fp);
if (!user_access_begin(frame, sizeof(*frame)))
return -EFAULT;
unsafe_put_user(ksig->sig, &frame->sig, Efault);
unsafe_put_user(ptr_to_compat(&frame->info), &frame->pinfo, Efault);
unsafe_put_user(ptr_to_compat(&frame->uc), &frame->puc, Efault);
/* Create the ucontext. */
if (static_cpu_has(X86_FEATURE_XSAVE))
unsafe_put_user(UC_FP_XSTATE, &frame->uc.uc_flags, Efault);
else
unsafe_put_user(0, &frame->uc.uc_flags, Efault);
unsafe_put_user(0, &frame->uc.uc_link, Efault);
unsafe_save_altstack32(&frame->uc.uc_stack, regs->sp, Efault);
if (ksig->ka.sa.sa_flags & SA_RESTORER)
restorer = ksig->ka.sa.sa_restorer;
else
restorer = current->mm->context.vdso +
vdso_image_32.sym___kernel_rt_sigreturn;
unsafe_put_user(ptr_to_compat(restorer), &frame->pretcode, Efault);
/*
* Not actually used anymore, but left because some gdb
* versions need it.
*/
unsafe_put_user(*((u64 *)&code), (u64 __user *)frame->retcode, Efault);
unsafe_put_sigcontext32(&frame->uc.uc_mcontext, fp, regs, set, Efault);
unsafe_put_user(*(__u64 *)set, (__u64 __user *)&frame->uc.uc_sigmask, Efault);
user_access_end();
if (__copy_siginfo_to_user32(&frame->info, &ksig->info))
return -EFAULT;
/* Set up registers for signal handler */
regs->sp = (unsigned long) frame;
regs->ip = (unsigned long) ksig->ka.sa.sa_handler;
/* Make -mregparm=3 work */
regs->ax = ksig->sig;
regs->dx = (unsigned long) &frame->info;
regs->cx = (unsigned long) &frame->uc;
#ifdef CONFIG_IA32_EMULATION
loadsegment(ds, __USER_DS);
loadsegment(es, __USER_DS);
#else
regs->ds = __USER_DS;
regs->es = __USER_DS;
#endif
regs->cs = __USER32_CS;
regs->ss = __USER_DS;
return 0;
Efault:
user_access_end();
return -EFAULT;
}
/*
* The 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 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.
*/
/*
* 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()!
*/
static_assert(NSIGILL == 11);
static_assert(NSIGFPE == 15);
static_assert(NSIGSEGV == 10);
static_assert(NSIGBUS == 5);
static_assert(NSIGTRAP == 6);
static_assert(NSIGCHLD == 6);
static_assert(NSIGSYS == 2);
/* This is part of the ABI and can never change in size: */
static_assert(sizeof(siginfo32_t) == 128);
/* This is a part of the ABI and can never change in alignment */
static_assert(__alignof__(siginfo32_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:
*/
static_assert(offsetof(siginfo32_t, _sifields) == 3 * sizeof(int));
static_assert(offsetof(siginfo32_t, si_signo) == 0);
static_assert(offsetof(siginfo32_t, si_errno) == 4);
static_assert(offsetof(siginfo32_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_SI_OFFSET(name) \
static_assert(offsetof(siginfo32_t, _sifields) == \
offsetof(siginfo32_t, _sifields.name))
#define CHECK_SI_SIZE(name, size) \
static_assert(sizeof_field(siginfo32_t, _sifields.name) == size)
CHECK_SI_OFFSET(_kill);
CHECK_SI_SIZE (_kill, 2*sizeof(int));
static_assert(offsetof(siginfo32_t, si_pid) == 0xC);
static_assert(offsetof(siginfo32_t, si_uid) == 0x10);
CHECK_SI_OFFSET(_timer);
#ifdef CONFIG_COMPAT
/* compat_siginfo_t doesn't have si_sys_private */
CHECK_SI_SIZE (_timer, 3*sizeof(int));
#else
CHECK_SI_SIZE (_timer, 4*sizeof(int));
#endif
static_assert(offsetof(siginfo32_t, si_tid) == 0x0C);
static_assert(offsetof(siginfo32_t, si_overrun) == 0x10);
static_assert(offsetof(siginfo32_t, si_value) == 0x14);
CHECK_SI_OFFSET(_rt);
CHECK_SI_SIZE (_rt, 3*sizeof(int));
static_assert(offsetof(siginfo32_t, si_pid) == 0x0C);
static_assert(offsetof(siginfo32_t, si_uid) == 0x10);
static_assert(offsetof(siginfo32_t, si_value) == 0x14);
CHECK_SI_OFFSET(_sigchld);
CHECK_SI_SIZE (_sigchld, 5*sizeof(int));
static_assert(offsetof(siginfo32_t, si_pid) == 0x0C);
static_assert(offsetof(siginfo32_t, si_uid) == 0x10);
static_assert(offsetof(siginfo32_t, si_status) == 0x14);
static_assert(offsetof(siginfo32_t, si_utime) == 0x18);
static_assert(offsetof(siginfo32_t, si_stime) == 0x1C);
CHECK_SI_OFFSET(_sigfault);
CHECK_SI_SIZE (_sigfault, 4*sizeof(int));
static_assert(offsetof(siginfo32_t, si_addr) == 0x0C);
static_assert(offsetof(siginfo32_t, si_trapno) == 0x10);
static_assert(offsetof(siginfo32_t, si_addr_lsb) == 0x10);
static_assert(offsetof(siginfo32_t, si_lower) == 0x14);
static_assert(offsetof(siginfo32_t, si_upper) == 0x18);
static_assert(offsetof(siginfo32_t, si_pkey) == 0x14);
static_assert(offsetof(siginfo32_t, si_perf_data) == 0x10);
static_assert(offsetof(siginfo32_t, si_perf_type) == 0x14);
static_assert(offsetof(siginfo32_t, si_perf_flags) == 0x18);
CHECK_SI_OFFSET(_sigpoll);
CHECK_SI_SIZE (_sigpoll, 2*sizeof(int));
static_assert(offsetof(siginfo32_t, si_band) == 0x0C);
static_assert(offsetof(siginfo32_t, si_fd) == 0x10);
CHECK_SI_OFFSET(_sigsys);
CHECK_SI_SIZE (_sigsys, 3*sizeof(int));
static_assert(offsetof(siginfo32_t, si_call_addr) == 0x0C);
static_assert(offsetof(siginfo32_t, si_syscall) == 0x10);
static_assert(offsetof(siginfo32_t, si_arch) == 0x14);
/* any new si_fields should be added here */
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