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linux/arch/x86/kernel/signal_64.c
Aruna Ramakrishna d10b554919 x86/pkeys: Restore altstack access in sigreturn() 
A process can disable access to the alternate signal stack by not
enabling the altstack's PKEY in the PKRU register.

Nevertheless, the kernel updates the PKRU temporarily for signal
handling. However, in sigreturn(), restore_sigcontext() will restore the
PKRU to the user-defined PKRU value.

This will cause restore_altstack() to fail with a SIGSEGV as it needs read
access to the altstack which is prohibited by the user-defined PKRU value.

Fix this by restoring altstack before restoring PKRU.

Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240802061318.2140081-5-aruna.ramakrishna@oracle.com
2024-08-02 14:12:21 +02:00

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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright (C) 2000, 2001, 2002 Andi Kleen SuSE Labs
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/unistd.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <asm/ucontext.h>
#include <asm/fpu/signal.h>
#include <asm/sighandling.h>
#include <asm/syscall.h>
#include <asm/sigframe.h>
#include <asm/signal.h>
/*
* If regs->ss will cause an IRET fault, change it. Otherwise leave it
* alone. Using this generally makes no sense unless
* user_64bit_mode(regs) would return true.
*/
static void force_valid_ss(struct pt_regs *regs)
{
u32 ar;
asm volatile ("lar %[old_ss], %[ar]\n\t"
"jz 1f\n\t" /* If invalid: */
"xorl %[ar], %[ar]\n\t" /* set ar = 0 */
"1:"
: [ar] "=r" (ar)
: [old_ss] "rm" ((u16)regs->ss));
/*
* For a valid 64-bit user context, we need DPL 3, type
* read-write data or read-write exp-down data, and S and P
* set. We can't use VERW because VERW doesn't check the
* P bit.
*/
ar &= AR_DPL_MASK | AR_S | AR_P | AR_TYPE_MASK;
if (ar != (AR_DPL3 | AR_S | AR_P | AR_TYPE_RWDATA) &&
ar != (AR_DPL3 | AR_S | AR_P | AR_TYPE_RWDATA_EXPDOWN))
regs->ss = __USER_DS;
}
static bool restore_sigcontext(struct pt_regs *regs,
struct sigcontext __user *usc,
unsigned long uc_flags)
{
struct sigcontext sc;
/* Always make any pending restarted system calls return -EINTR */
current->restart_block.fn = do_no_restart_syscall;
if (copy_from_user(&sc, usc, offsetof(struct sigcontext, reserved1)))
return false;
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;
regs->r8 = sc.r8;
regs->r9 = sc.r9;
regs->r10 = sc.r10;
regs->r11 = sc.r11;
regs->r12 = sc.r12;
regs->r13 = sc.r13;
regs->r14 = sc.r14;
regs->r15 = sc.r15;
/* 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;
/*
* Fix up SS if needed for the benefit of old DOSEMU and
* CRIU.
*/
if (unlikely(!(uc_flags & UC_STRICT_RESTORE_SS) && user_64bit_mode(regs)))
force_valid_ss(regs);
return fpu__restore_sig((void __user *)sc.fpstate, 0);
}
static __always_inline int
__unsafe_setup_sigcontext(struct sigcontext __user *sc, void __user *fpstate,
struct pt_regs *regs, unsigned long mask)
{
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(regs->r8, &sc->r8, Efault);
unsafe_put_user(regs->r9, &sc->r9, Efault);
unsafe_put_user(regs->r10, &sc->r10, Efault);
unsafe_put_user(regs->r11, &sc->r11, Efault);
unsafe_put_user(regs->r12, &sc->r12, Efault);
unsafe_put_user(regs->r13, &sc->r13, Efault);
unsafe_put_user(regs->r14, &sc->r14, Efault);
unsafe_put_user(regs->r15, &sc->r15, 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->flags, &sc->flags, Efault);
unsafe_put_user(regs->cs, &sc->cs, Efault);
unsafe_put_user(0, &sc->gs, Efault);
unsafe_put_user(0, &sc->fs, Efault);
unsafe_put_user(regs->ss, &sc->ss, Efault);
unsafe_put_user(fpstate, (unsigned long __user *)&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_sigcontext(sc, fp, regs, set, label) \
do { \
if (__unsafe_setup_sigcontext(sc, fp, regs, set->sig[0])) \
goto label; \
} while(0);
#define unsafe_put_sigmask(set, frame, label) \
unsafe_put_user(*(__u64 *)(set), \
(__u64 __user *)&(frame)->uc.uc_sigmask, \
label)
static unsigned long frame_uc_flags(struct pt_regs *regs)
{
unsigned long flags;
if (boot_cpu_has(X86_FEATURE_XSAVE))
flags = UC_FP_XSTATE | UC_SIGCONTEXT_SS;
else
flags = UC_SIGCONTEXT_SS;
if (likely(user_64bit_mode(regs)))
flags |= UC_STRICT_RESTORE_SS;
return flags;
}
int x64_setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
{
sigset_t *set = sigmask_to_save();
struct rt_sigframe __user *frame;
void __user *fp = NULL;
unsigned long uc_flags;
/* x86-64 should always use SA_RESTORER. */
if (!(ksig->ka.sa.sa_flags & SA_RESTORER))
return -EFAULT;
frame = get_sigframe(ksig, regs, sizeof(struct rt_sigframe), &fp);
uc_flags = frame_uc_flags(regs);
if (!user_access_begin(frame, sizeof(*frame)))
return -EFAULT;
/* Create the ucontext. */
unsafe_put_user(uc_flags, &frame->uc.uc_flags, Efault);
unsafe_put_user(0, &frame->uc.uc_link, Efault);
unsafe_save_altstack(&frame->uc.uc_stack, regs->sp, Efault);
/* Set up to return from userspace. If provided, use a stub
already in userspace. */
unsafe_put_user(ksig->ka.sa.sa_restorer, &frame->pretcode, Efault);
unsafe_put_sigcontext(&frame->uc.uc_mcontext, fp, regs, set, Efault);
unsafe_put_sigmask(set, frame, Efault);
user_access_end();
if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
if (copy_siginfo_to_user(&frame->info, &ksig->info))
return -EFAULT;
}
if (setup_signal_shadow_stack(ksig))
return -EFAULT;
/* Set up registers for signal handler */
regs->di = ksig->sig;
/* In case the signal handler was declared without prototypes */
regs->ax = 0;
/* This also works for non SA_SIGINFO handlers because they expect the
next argument after the signal number on the stack. */
regs->si = (unsigned long)&frame->info;
regs->dx = (unsigned long)&frame->uc;
regs->ip = (unsigned long) ksig->ka.sa.sa_handler;
regs->sp = (unsigned long)frame;
/*
* Set up the CS and SS registers to run signal handlers in
* 64-bit mode, even if the handler happens to be interrupting
* 32-bit or 16-bit code.
*
* SS is subtle. In 64-bit mode, we don't need any particular
* SS descriptor, but we do need SS to be valid. It's possible
* that the old SS is entirely bogus -- this can happen if the
* signal we're trying to deliver is #GP or #SS caused by a bad
* SS value. We also have a compatibility issue here: DOSEMU
* relies on the contents of the SS register indicating the
* SS value at the time of the signal, even though that code in
* DOSEMU predates sigreturn's ability to restore SS. (DOSEMU
* avoids relying on sigreturn to restore SS; instead it uses
* a trampoline.) So we do our best: if the old SS was valid,
* we keep it. Otherwise we replace it.
*/
regs->cs = __USER_CS;
if (unlikely(regs->ss != __USER_DS))
force_valid_ss(regs);
return 0;
Efault:
user_access_end();
return -EFAULT;
}
/*
* Do a signal return; undo the signal stack.
*/
SYSCALL_DEFINE0(rt_sigreturn)
{
struct pt_regs *regs = current_pt_regs();
struct rt_sigframe __user *frame;
sigset_t set;
unsigned long uc_flags;
frame = (struct rt_sigframe __user *)(regs->sp - sizeof(long));
if (!access_ok(frame, sizeof(*frame)))
goto badframe;
if (__get_user(*(__u64 *)&set, (__u64 __user *)&frame->uc.uc_sigmask))
goto badframe;
if (__get_user(uc_flags, &frame->uc.uc_flags))
goto badframe;
set_current_blocked(&set);
if (restore_altstack(&frame->uc.uc_stack))
goto badframe;
if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
if (restore_signal_shadow_stack())
goto badframe;
return regs->ax;
badframe:
signal_fault(regs, frame, "rt_sigreturn");
return 0;
}
#ifdef CONFIG_X86_X32_ABI
static int x32_copy_siginfo_to_user(struct compat_siginfo __user *to,
const struct kernel_siginfo *from)
{
struct compat_siginfo new;
copy_siginfo_to_external32(&new, from);
if (from->si_signo == SIGCHLD) {
new._sifields._sigchld_x32._utime = from->si_utime;
new._sifields._sigchld_x32._stime = from->si_stime;
}
if (copy_to_user(to, &new, sizeof(struct compat_siginfo)))
return -EFAULT;
return 0;
}
int copy_siginfo_to_user32(struct compat_siginfo __user *to,
const struct kernel_siginfo *from)
{
if (in_x32_syscall())
return x32_copy_siginfo_to_user(to, from);
return __copy_siginfo_to_user32(to, from);
}
int x32_setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
{
compat_sigset_t *set = (compat_sigset_t *) sigmask_to_save();
struct rt_sigframe_x32 __user *frame;
unsigned long uc_flags;
void __user *restorer;
void __user *fp = NULL;
if (!(ksig->ka.sa.sa_flags & SA_RESTORER))
return -EFAULT;
frame = get_sigframe(ksig, regs, sizeof(*frame), &fp);
uc_flags = frame_uc_flags(regs);
if (setup_signal_shadow_stack(ksig))
return -EFAULT;
if (!user_access_begin(frame, sizeof(*frame)))
return -EFAULT;
/* Create the ucontext. */
unsafe_put_user(uc_flags, &frame->uc.uc_flags, Efault);
unsafe_put_user(0, &frame->uc.uc_link, Efault);
unsafe_compat_save_altstack(&frame->uc.uc_stack, regs->sp, Efault);
unsafe_put_user(0, &frame->uc.uc__pad0, Efault);
restorer = ksig->ka.sa.sa_restorer;
unsafe_put_user(restorer, (unsigned long __user *)&frame->pretcode, Efault);
unsafe_put_sigcontext(&frame->uc.uc_mcontext, fp, regs, set, Efault);
unsafe_put_sigmask(set, frame, Efault);
user_access_end();
if (ksig->ka.sa.sa_flags & SA_SIGINFO) {
if (x32_copy_siginfo_to_user(&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;
/* We use the x32 calling convention here... */
regs->di = ksig->sig;
regs->si = (unsigned long) &frame->info;
regs->dx = (unsigned long) &frame->uc;
loadsegment(ds, __USER_DS);
loadsegment(es, __USER_DS);
regs->cs = __USER_CS;
regs->ss = __USER_DS;
return 0;
Efault:
user_access_end();
return -EFAULT;
}
COMPAT_SYSCALL_DEFINE0(x32_rt_sigreturn)
{
struct pt_regs *regs = current_pt_regs();
struct rt_sigframe_x32 __user *frame;
sigset_t set;
unsigned long uc_flags;
frame = (struct rt_sigframe_x32 __user *)(regs->sp - 8);
if (!access_ok(frame, sizeof(*frame)))
goto badframe;
if (__get_user(set.sig[0], (__u64 __user *)&frame->uc.uc_sigmask))
goto badframe;
if (__get_user(uc_flags, &frame->uc.uc_flags))
goto badframe;
set_current_blocked(&set);
if (!restore_sigcontext(regs, &frame->uc.uc_mcontext, uc_flags))
goto badframe;
if (restore_signal_shadow_stack())
goto badframe;
if (compat_restore_altstack(&frame->uc.uc_stack))
goto badframe;
return regs->ax;
badframe:
signal_fault(regs, frame, "x32 rt_sigreturn");
return 0;
}
#endif /* CONFIG_X86_X32_ABI */
#ifdef CONFIG_COMPAT
void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact)
{
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;
}
#endif /* CONFIG_COMPAT */
/*
* 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(siginfo_t) == 128);
/* This is a part of the ABI and can never change in alignment */
static_assert(__alignof__(siginfo_t) == 8);
/*
* 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(siginfo_t, si_signo) == 0);
static_assert(offsetof(siginfo_t, si_errno) == 4);
static_assert(offsetof(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_SI_OFFSET(name) \
static_assert(offsetof(siginfo_t, _sifields) == \
offsetof(siginfo_t, _sifields.name))
#define CHECK_SI_SIZE(name, size) \
static_assert(sizeof_field(siginfo_t, _sifields.name) == size)
CHECK_SI_OFFSET(_kill);
CHECK_SI_SIZE (_kill, 2*sizeof(int));
static_assert(offsetof(siginfo_t, si_pid) == 0x10);
static_assert(offsetof(siginfo_t, si_uid) == 0x14);
CHECK_SI_OFFSET(_timer);
CHECK_SI_SIZE (_timer, 6*sizeof(int));
static_assert(offsetof(siginfo_t, si_tid) == 0x10);
static_assert(offsetof(siginfo_t, si_overrun) == 0x14);
static_assert(offsetof(siginfo_t, si_value) == 0x18);
CHECK_SI_OFFSET(_rt);
CHECK_SI_SIZE (_rt, 4*sizeof(int));
static_assert(offsetof(siginfo_t, si_pid) == 0x10);
static_assert(offsetof(siginfo_t, si_uid) == 0x14);
static_assert(offsetof(siginfo_t, si_value) == 0x18);
CHECK_SI_OFFSET(_sigchld);
CHECK_SI_SIZE (_sigchld, 8*sizeof(int));
static_assert(offsetof(siginfo_t, si_pid) == 0x10);
static_assert(offsetof(siginfo_t, si_uid) == 0x14);
static_assert(offsetof(siginfo_t, si_status) == 0x18);
static_assert(offsetof(siginfo_t, si_utime) == 0x20);
static_assert(offsetof(siginfo_t, si_stime) == 0x28);
#ifdef CONFIG_X86_X32_ABI
/* no _sigchld_x32 in the generic siginfo_t */
static_assert(sizeof_field(compat_siginfo_t, _sifields._sigchld_x32) ==
7*sizeof(int));
static_assert(offsetof(compat_siginfo_t, _sifields) ==
offsetof(compat_siginfo_t, _sifields._sigchld_x32));
static_assert(offsetof(compat_siginfo_t, _sifields._sigchld_x32._utime) == 0x18);
static_assert(offsetof(compat_siginfo_t, _sifields._sigchld_x32._stime) == 0x20);
#endif
CHECK_SI_OFFSET(_sigfault);
CHECK_SI_SIZE (_sigfault, 8*sizeof(int));
static_assert(offsetof(siginfo_t, si_addr) == 0x10);
static_assert(offsetof(siginfo_t, si_trapno) == 0x18);
static_assert(offsetof(siginfo_t, si_addr_lsb) == 0x18);
static_assert(offsetof(siginfo_t, si_lower) == 0x20);
static_assert(offsetof(siginfo_t, si_upper) == 0x28);
static_assert(offsetof(siginfo_t, si_pkey) == 0x20);
static_assert(offsetof(siginfo_t, si_perf_data) == 0x18);
static_assert(offsetof(siginfo_t, si_perf_type) == 0x20);
static_assert(offsetof(siginfo_t, si_perf_flags) == 0x24);
CHECK_SI_OFFSET(_sigpoll);
CHECK_SI_SIZE (_sigpoll, 4*sizeof(int));
static_assert(offsetof(siginfo_t, si_band) == 0x10);
static_assert(offsetof(siginfo_t, si_fd) == 0x18);
CHECK_SI_OFFSET(_sigsys);
CHECK_SI_SIZE (_sigsys, 4*sizeof(int));
static_assert(offsetof(siginfo_t, si_call_addr) == 0x10);
static_assert(offsetof(siginfo_t, si_syscall) == 0x18);
static_assert(offsetof(siginfo_t, si_arch) == 0x1C);
/* any new si_fields should be added here */
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