diff options
| -rw-r--r-- | arch/x86/include/asm/mpx.h | 12 | ||||
| -rw-r--r-- | arch/x86/mm/mpx.c | 237 |
2 files changed, 249 insertions, 0 deletions
diff --git a/arch/x86/include/asm/mpx.h b/arch/x86/include/asm/mpx.h index 7d7c5f54cc5f..35bcb1cddf40 100644 --- a/arch/x86/include/asm/mpx.h +++ b/arch/x86/include/asm/mpx.h @@ -3,6 +3,7 @@ #include <linux/types.h> #include <asm/ptrace.h> +#include <asm/insn.h> #ifdef CONFIG_X86_64 @@ -33,4 +34,15 @@ #define MPX_BNDSTA_ERROR_CODE 0x3 +#ifdef CONFIG_X86_INTEL_MPX +siginfo_t *mpx_generate_siginfo(struct pt_regs *regs, + struct xsave_struct *xsave_buf); +#else +static inline siginfo_t *mpx_generate_siginfo(struct pt_regs *regs, + struct xsave_struct *xsave_buf) +{ + return NULL; +} +#endif /* CONFIG_X86_INTEL_MPX */ + #endif /* _ASM_X86_MPX_H */ diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 72d13b0779a2..9009e094d686 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -6,6 +6,7 @@ * Dave Hansen <dave.hansen@intel.com> */ #include <linux/kernel.h> +#include <linux/slab.h> #include <linux/syscalls.h> #include <linux/sched/sysctl.h> @@ -84,3 +85,239 @@ out: up_write(&mm->mmap_sem); return ret; } + +enum reg_type { + REG_TYPE_RM = 0, + REG_TYPE_INDEX, + REG_TYPE_BASE, +}; + +static unsigned long get_reg_offset(struct insn *insn, struct pt_regs *regs, + enum reg_type type) +{ + int regno = 0; + + static const int regoff[] = { + offsetof(struct pt_regs, ax), + offsetof(struct pt_regs, cx), + offsetof(struct pt_regs, dx), + offsetof(struct pt_regs, bx), + offsetof(struct pt_regs, sp), + offsetof(struct pt_regs, bp), + offsetof(struct pt_regs, si), + offsetof(struct pt_regs, di), +#ifdef CONFIG_X86_64 + offsetof(struct pt_regs, r8), + offsetof(struct pt_regs, r9), + offsetof(struct pt_regs, r10), + offsetof(struct pt_regs, r11), + offsetof(struct pt_regs, r12), + offsetof(struct pt_regs, r13), + offsetof(struct pt_regs, r14), + offsetof(struct pt_regs, r15), +#endif + }; + int nr_registers = ARRAY_SIZE(regoff); + /* + * Don't possibly decode a 32-bit instructions as + * reading a 64-bit-only register. + */ + if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64) + nr_registers -= 8; + + switch (type) { + case REG_TYPE_RM: + regno = X86_MODRM_RM(insn->modrm.value); + if (X86_REX_B(insn->rex_prefix.value) == 1) + regno += 8; + break; + + case REG_TYPE_INDEX: + regno = X86_SIB_INDEX(insn->sib.value); + if (X86_REX_X(insn->rex_prefix.value) == 1) + regno += 8; + break; + + case REG_TYPE_BASE: + regno = X86_SIB_BASE(insn->sib.value); + if (X86_REX_B(insn->rex_prefix.value) == 1) + regno += 8; + break; + + default: + pr_err("invalid register type"); + BUG(); + break; + } + + if (regno > nr_registers) { + WARN_ONCE(1, "decoded an instruction with an invalid register"); + return -EINVAL; + } + return regoff[regno]; +} + +/* + * return the address being referenced be instruction + * for rm=3 returning the content of the rm reg + * for rm!=3 calculates the address using SIB and Disp + */ +static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) +{ + unsigned long addr, addr_offset; + unsigned long base, base_offset; + unsigned long indx, indx_offset; + insn_byte_t sib; + + insn_get_modrm(insn); + insn_get_sib(insn); + sib = insn->sib.value; + + if (X86_MODRM_MOD(insn->modrm.value) == 3) { + addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); + if (addr_offset < 0) + goto out_err; + addr = regs_get_register(regs, addr_offset); + } else { + if (insn->sib.nbytes) { + base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE); + if (base_offset < 0) + goto out_err; + + indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); + if (indx_offset < 0) + goto out_err; + + base = regs_get_register(regs, base_offset); + indx = regs_get_register(regs, indx_offset); + addr = base + indx * (1 << X86_SIB_SCALE(sib)); + } else { + addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); + if (addr_offset < 0) + goto out_err; + addr = regs_get_register(regs, addr_offset); + } + addr += insn->displacement.value; + } + return (void __user *)addr; +out_err: + return (void __user *)-1; +} + +static int mpx_insn_decode(struct insn *insn, + struct pt_regs *regs) +{ + unsigned char buf[MAX_INSN_SIZE]; + int x86_64 = !test_thread_flag(TIF_IA32); + int not_copied; + int nr_copied; + + not_copied = copy_from_user(buf, (void __user *)regs->ip, sizeof(buf)); + nr_copied = sizeof(buf) - not_copied; + /* + * The decoder _should_ fail nicely if we pass it a short buffer. + * But, let's not depend on that implementation detail. If we + * did not get anything, just error out now. + */ + if (!nr_copied) + return -EFAULT; + insn_init(insn, buf, nr_copied, x86_64); + insn_get_length(insn); + /* + * copy_from_user() tries to get as many bytes as we could see in + * the largest possible instruction. If the instruction we are + * after is shorter than that _and_ we attempt to copy from + * something unreadable, we might get a short read. This is OK + * as long as the read did not stop in the middle of the + * instruction. Check to see if we got a partial instruction. + */ + if (nr_copied < insn->length) + return -EFAULT; + + insn_get_opcode(insn); + /* + * We only _really_ need to decode bndcl/bndcn/bndcu + * Error out on anything else. + */ + if (insn->opcode.bytes[0] != 0x0f) + goto bad_opcode; + if ((insn->opcode.bytes[1] != 0x1a) && + (insn->opcode.bytes[1] != 0x1b)) + goto bad_opcode; + + return 0; +bad_opcode: + return -EINVAL; +} + +/* + * If a bounds overflow occurs then a #BR is generated. This + * function decodes MPX instructions to get violation address + * and set this address into extended struct siginfo. + * + * Note that this is not a super precise way of doing this. + * Userspace could have, by the time we get here, written + * anything it wants in to the instructions. We can not + * trust anything about it. They might not be valid + * instructions or might encode invalid registers, etc... + * + * The caller is expected to kfree() the returned siginfo_t. + */ +siginfo_t *mpx_generate_siginfo(struct pt_regs *regs, + struct xsave_struct *xsave_buf) +{ + struct insn insn; + uint8_t bndregno; + int err; + siginfo_t *info; + + err = mpx_insn_decode(&insn, regs); + if (err) + goto err_out; + + /* + * We know at this point that we are only dealing with + * MPX instructions. + */ + insn_get_modrm(&insn); + bndregno = X86_MODRM_REG(insn.modrm.value); + if (bndregno > 3) { + err = -EINVAL; + goto err_out; + } + info = kzalloc(sizeof(*info), GFP_KERNEL); + if (!info) { + err = -ENOMEM; + goto err_out; + } + /* + * The registers are always 64-bit, but the upper 32 + * bits are ignored in 32-bit mode. Also, note that the + * upper bounds are architecturally represented in 1's + * complement form. + * + * The 'unsigned long' cast is because the compiler + * complains when casting from integers to different-size + * pointers. + */ + info->si_lower = (void __user *)(unsigned long) + (xsave_buf->bndreg[bndregno].lower_bound); + info->si_upper = (void __user *)(unsigned long) + (~xsave_buf->bndreg[bndregno].upper_bound); + info->si_addr_lsb = 0; + info->si_signo = SIGSEGV; + info->si_errno = 0; + info->si_code = SEGV_BNDERR; + info->si_addr = mpx_get_addr_ref(&insn, regs); + /* + * We were not able to extract an address from the instruction, + * probably because there was something invalid in it. + */ + if (info->si_addr == (void *)-1) { + err = -EINVAL; + goto err_out; + } + return info; +err_out: + return ERR_PTR(err); +} |