diff options
Diffstat (limited to 'arch/x86/kernel/signal_32.c')
| -rw-r--r-- | arch/x86/kernel/signal_32.c | 196 |
1 files changed, 176 insertions, 20 deletions
diff --git a/arch/x86/kernel/signal_32.c b/arch/x86/kernel/signal_32.c index 2553136cf39b..42bbc42bd350 100644 --- a/arch/x86/kernel/signal_32.c +++ b/arch/x86/kernel/signal_32.c @@ -31,35 +31,68 @@ #include <asm/sigframe.h> #include <asm/sighandling.h> #include <asm/smap.h> +#include <asm/gsseg.h> + +/* + * The first GDT descriptor is reserved as 'NULL descriptor'. As bits 0 + * and 1 of a segment selector, i.e., the RPL bits, are NOT used to index + * GDT, selector values 0~3 all point to the NULL descriptor, thus values + * 0, 1, 2 and 3 are all valid NULL selector values. + * + * However IRET zeros ES, FS, GS, and DS segment registers if any of them + * is found to have any nonzero NULL selector value, which can be used by + * userspace in pre-FRED systems to spot any interrupt/exception by loading + * a nonzero NULL selector and waiting for it to become zero. Before FRED + * there was nothing software could do to prevent such an information leak. + * + * ERETU, the only legit instruction to return to userspace from kernel + * under FRED, by design does NOT zero any segment register to avoid this + * problem behavior. + * + * As such, leave NULL selector values 0~3 unchanged. + */ +static inline u16 fixup_rpl(u16 sel) +{ + return sel <= 3 ? sel : sel | 3; +} #ifdef CONFIG_IA32_EMULATION -#include <asm/ia32_unistd.h> +#include <asm/unistd_32_ia32.h> static inline void reload_segments(struct sigcontext_32 *sc) { - unsigned int cur; + u16 cur; + /* + * 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. + */ savesegment(gs, cur); - if ((sc->gs | 0x03) != cur) - load_gs_index(sc->gs | 0x03); + if (fixup_rpl(sc->gs) != cur) + load_gs_index(fixup_rpl(sc->gs)); savesegment(fs, cur); - if ((sc->fs | 0x03) != cur) - loadsegment(fs, sc->fs | 0x03); + if (fixup_rpl(sc->fs) != cur) + loadsegment(fs, fixup_rpl(sc->fs)); + savesegment(ds, cur); - if ((sc->ds | 0x03) != cur) - loadsegment(ds, sc->ds | 0x03); + if (fixup_rpl(sc->ds) != cur) + loadsegment(ds, fixup_rpl(sc->ds)); savesegment(es, cur); - if ((sc->es | 0x03) != cur) - loadsegment(es, sc->es | 0x03); + if (fixup_rpl(sc->es) != cur) + loadsegment(es, fixup_rpl(sc->es)); } #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 @@ -102,18 +135,12 @@ static bool ia32_restore_sigcontext(struct pt_regs *regs, 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; + loadsegment(gs, fixup_rpl(sc.gs)); + regs->fs = fixup_rpl(sc.fs); + regs->es = fixup_rpl(sc.es); + regs->ds = fixup_rpl(sc.ds); #endif return fpu__restore_sig(compat_ptr(sc.fpstate), 1); @@ -125,6 +152,8 @@ SYSCALL32_DEFINE0(sigreturn) struct sigframe_ia32 __user *frame = (struct sigframe_ia32 __user *)(regs->sp-8); sigset_t set; + prevent_single_step_upon_eretu(regs); + if (!access_ok(frame, sizeof(*frame))) goto badframe; if (__get_user(set.sig[0], &frame->sc.oldmask) @@ -148,6 +177,8 @@ SYSCALL32_DEFINE0(rt_sigreturn) struct rt_sigframe_ia32 __user *frame; sigset_t set; + prevent_single_step_upon_eretu(regs); + frame = (struct rt_sigframe_ia32 __user *)(regs->sp - 4); if (!access_ok(frame, sizeof(*frame))) @@ -377,3 +408,128 @@ 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 */ |