1 files changed, 387 insertions, 0 deletions
diff --git a/arch/arm64/kernel/compat_alignment.c b/arch/arm64/kernel/compat_alignment.c
new file mode 100644
index 000000000000..5edec2f49ec9
--- /dev/null
+++ b/arch/arm64/kernel/compat_alignment.c
@@ -0,0 +1,387 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// based on arch/arm/mm/alignment.c
+
+#include <linux/compiler.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/perf_event.h>
+#include <linux/uaccess.h>
+
+#include <asm/exception.h>
+#include <asm/ptrace.h>
+#include <asm/traps.h>
+
+/*
+ * 32-bit misaligned trap handler (c) 1998 San Mehat (CCC) -July 1998
+ *
+ * Speed optimisations and better fault handling by Russell King.
+ */
+#define CODING_BITS(i)	(i & 0x0e000000)
+
+#define LDST_P_BIT(i)	(i & (1 << 24))		/* Preindex		*/
+#define LDST_U_BIT(i)	(i & (1 << 23))		/* Add offset		*/
+#define LDST_W_BIT(i)	(i & (1 << 21))		/* Writeback		*/
+#define LDST_L_BIT(i)	(i & (1 << 20))		/* Load			*/
+
+#define LDST_P_EQ_U(i)	((((i) ^ ((i) >> 1)) & (1 << 23)) == 0)
+
+#define LDSTHD_I_BIT(i)	(i & (1 << 22))		/* double/half-word immed */
+
+#define RN_BITS(i)	((i >> 16) & 15)	/* Rn			*/
+#define RD_BITS(i)	((i >> 12) & 15)	/* Rd			*/
+#define RM_BITS(i)	(i & 15)		/* Rm			*/
+
+#define REGMASK_BITS(i)	(i & 0xffff)
+
+#define BAD_INSTR 	0xdeadc0de
+
+/* Thumb-2 32 bit format per ARMv7 DDI0406A A6.3, either f800h,e800h,f800h */
+#define IS_T32(hi16) \
+	(((hi16) & 0xe000) == 0xe000 && ((hi16) & 0x1800))
+
+union offset_union {
+	unsigned long un;
+	  signed long sn;
+};
+
+#define TYPE_ERROR	0
+#define TYPE_FAULT	1
+#define TYPE_LDST	2
+#define TYPE_DONE	3
+
+static void
+do_alignment_finish_ldst(unsigned long addr, u32 instr, struct pt_regs *regs,
+			 union offset_union offset)
+{
+	if (!LDST_U_BIT(instr))
+		offset.un = -offset.un;
+
+	if (!LDST_P_BIT(instr))
+		addr += offset.un;
+
+	if (!LDST_P_BIT(instr) || LDST_W_BIT(instr))
+		regs->regs[RN_BITS(instr)] = addr;
+}
+
+static int
+do_alignment_ldrdstrd(unsigned long addr, u32 instr, struct pt_regs *regs)
+{
+	unsigned int rd = RD_BITS(instr);
+	unsigned int rd2;
+	int load;
+
+	if ((instr & 0xfe000000) == 0xe8000000) {
+		/* ARMv7 Thumb-2 32-bit LDRD/STRD */
+		rd2 = (instr >> 8) & 0xf;
+		load = !!(LDST_L_BIT(instr));
+	} else if (((rd & 1) == 1) || (rd == 14)) {
+		return TYPE_ERROR;
+	} else {
+		load = ((instr & 0xf0) == 0xd0);
+		rd2 = rd + 1;
+	}
+
+	if (load) {
+		unsigned int val, val2;
+
+		if (get_user(val, (u32 __user *)addr) ||
+		    get_user(val2, (u32 __user *)(addr + 4)))
+			return TYPE_FAULT;
+		regs->regs[rd] = val;
+		regs->regs[rd2] = val2;
+	} else {
+		if (put_user(regs->regs[rd], (u32 __user *)addr) ||
+		    put_user(regs->regs[rd2], (u32 __user *)(addr + 4)))
+			return TYPE_FAULT;
+	}
+	return TYPE_LDST;
+}
+
+/*
+ * LDM/STM alignment handler.
+ *
+ * There are 4 variants of this instruction:
+ *
+ * B = rn pointer before instruction, A = rn pointer after instruction
+ *              ------ increasing address ----->
+ *	        |    | r0 | r1 | ... | rx |    |
+ * PU = 01             B                    A
+ * PU = 11        B                    A
+ * PU = 00        A                    B
+ * PU = 10             A                    B
+ */
+static int
+do_alignment_ldmstm(unsigned long addr, u32 instr, struct pt_regs *regs)
+{
+	unsigned int rd, rn, nr_regs, regbits;
+	unsigned long eaddr, newaddr;
+	unsigned int val;
+
+	/* count the number of registers in the mask to be transferred */
+	nr_regs = hweight16(REGMASK_BITS(instr)) * 4;
+
+	rn = RN_BITS(instr);
+	newaddr = eaddr = regs->regs[rn];
+
+	if (!LDST_U_BIT(instr))
+		nr_regs = -nr_regs;
+	newaddr += nr_regs;
+	if (!LDST_U_BIT(instr))
+		eaddr = newaddr;
+
+	if (LDST_P_EQ_U(instr))	/* U = P */
+		eaddr += 4;
+
+	for (regbits = REGMASK_BITS(instr), rd = 0; regbits;
+	     regbits >>= 1, rd += 1)
+		if (regbits & 1) {
+			if (LDST_L_BIT(instr)) {
+				if (get_user(val, (u32 __user *)eaddr))
+					return TYPE_FAULT;
+				if (rd < 15)
+					regs->regs[rd] = val;
+				else
+					regs->pc = val;
+			} else {
+				/*
+				 * The PC register has a bias of +8 in ARM mode
+				 * and +4 in Thumb mode. This means that a read
+				 * of the value of PC should account for this.
+				 * Since Thumb does not permit STM instructions
+				 * to refer to PC, just add 8 here.
+				 */
+				val = (rd < 15) ? regs->regs[rd] : regs->pc + 8;
+				if (put_user(val, (u32 __user *)eaddr))
+					return TYPE_FAULT;
+			}
+			eaddr += 4;
+		}
+
+	if (LDST_W_BIT(instr))
+		regs->regs[rn] = newaddr;
+
+	return TYPE_DONE;
+}
+
+/*
+ * Convert Thumb multi-word load/store instruction forms to equivalent ARM
+ * instructions so we can reuse ARM userland alignment fault fixups for Thumb.
+ *
+ * This implementation was initially based on the algorithm found in
+ * gdb/sim/arm/thumbemu.c. It is basically just a code reduction of same
+ * to convert only Thumb ld/st instruction forms to equivalent ARM forms.
+ *
+ * NOTES:
+ * 1. Comments below refer to ARM ARM DDI0100E Thumb Instruction sections.
+ * 2. If for some reason we're passed an non-ld/st Thumb instruction to
+ *    decode, we return 0xdeadc0de. This should never happen under normal
+ *    circumstances but if it does, we've got other problems to deal with
+ *    elsewhere and we obviously can't fix those problems here.
+ */
+
+static unsigned long thumb2arm(u16 tinstr)
+{
+	u32 L = (tinstr & (1<<11)) >> 11;
+
+	switch ((tinstr & 0xf800) >> 11) {
+	/* 6.6.1 Format 1: */
+	case 0xc000 >> 11:				/* 7.1.51 STMIA */
+	case 0xc800 >> 11:				/* 7.1.25 LDMIA */
+		{
+			u32 Rn = (tinstr & (7<<8)) >> 8;
+			u32 W = ((L<<Rn) & (tinstr&255)) ? 0 : 1<<21;
+
+			return 0xe8800000 | W | (L<<20) | (Rn<<16) |
+				(tinstr&255);
+		}
+
+	/* 6.6.1 Format 2: */
+	case 0xb000 >> 11:				/* 7.1.48 PUSH */
+	case 0xb800 >> 11:				/* 7.1.47 POP */
+		if ((tinstr & (3 << 9)) == 0x0400) {
+			static const u32 subset[4] = {
+				0xe92d0000,	/* STMDB sp!,{registers} */
+				0xe92d4000,	/* STMDB sp!,{registers,lr} */
+				0xe8bd0000,	/* LDMIA sp!,{registers} */
+				0xe8bd8000	/* LDMIA sp!,{registers,pc} */
+			};
+			return subset[(L<<1) | ((tinstr & (1<<8)) >> 8)] |
+			    (tinstr & 255);		/* register_list */
+		}
+		fallthrough;	/* for illegal instruction case */
+
+	default:
+		return BAD_INSTR;
+	}
+}
+
+/*
+ * Convert Thumb-2 32 bit LDM, STM, LDRD, STRD to equivalent instruction
+ * handlable by ARM alignment handler, also find the corresponding handler,
+ * so that we can reuse ARM userland alignment fault fixups for Thumb.
+ *
+ * @pinstr: original Thumb-2 instruction; returns new handlable instruction
+ * @regs: register context.
+ * @poffset: return offset from faulted addr for later writeback
+ *
+ * NOTES:
+ * 1. Comments below refer to ARMv7 DDI0406A Thumb Instruction sections.
+ * 2. Register name Rt from ARMv7 is same as Rd from ARMv6 (Rd is Rt)
+ */
+static void *
+do_alignment_t32_to_handler(u32 *pinstr, struct pt_regs *regs,
+			    union offset_union *poffset)
+{
+	u32 instr = *pinstr;
+	u16 tinst1 = (instr >> 16) & 0xffff;
+	u16 tinst2 = instr & 0xffff;
+
+	switch (tinst1 & 0xffe0) {
+	/* A6.3.5 Load/Store multiple */
+	case 0xe880:		/* STM/STMIA/STMEA,LDM/LDMIA, PUSH/POP T2 */
+	case 0xe8a0:		/* ...above writeback version */
+	case 0xe900:		/* STMDB/STMFD, LDMDB/LDMEA */
+	case 0xe920:		/* ...above writeback version */
+		/* no need offset decision since handler calculates it */
+		return do_alignment_ldmstm;
+
+	case 0xf840:		/* POP/PUSH T3 (single register) */
+		if (RN_BITS(instr) == 13 && (tinst2 & 0x09ff) == 0x0904) {
+			u32 L = !!(LDST_L_BIT(instr));
+			const u32 subset[2] = {
+				0xe92d0000,	/* STMDB sp!,{registers} */
+				0xe8bd0000,	/* LDMIA sp!,{registers} */
+			};
+			*pinstr = subset[L] | (1<<RD_BITS(instr));
+			return do_alignment_ldmstm;
+		}
+		/* Else fall through for illegal instruction case */
+		break;
+
+	/* A6.3.6 Load/store double, STRD/LDRD(immed, lit, reg) */
+	case 0xe860:
+	case 0xe960:
+	case 0xe8e0:
+	case 0xe9e0:
+		poffset->un = (tinst2 & 0xff) << 2;
+		fallthrough;
+
+	case 0xe940:
+	case 0xe9c0:
+		return do_alignment_ldrdstrd;
+
+	/*
+	 * No need to handle load/store instructions up to word size
+	 * since ARMv6 and later CPUs can perform unaligned accesses.
+	 */
+	default:
+		break;
+	}
+	return NULL;
+}
+
+static int alignment_get_arm(struct pt_regs *regs, __le32 __user *ip, u32 *inst)
+{
+	__le32 instr = 0;
+	int fault;
+
+	fault = get_user(instr, ip);
+	if (fault)
+		return fault;
+
+	*inst = __le32_to_cpu(instr);
+	return 0;
+}
+
+static int alignment_get_thumb(struct pt_regs *regs, __le16 __user *ip, u16 *inst)
+{
+	__le16 instr = 0;
+	int fault;
+
+	fault = get_user(instr, ip);
+	if (fault)
+		return fault;
+
+	*inst = __le16_to_cpu(instr);
+	return 0;
+}
+
+int do_compat_alignment_fixup(unsigned long addr, struct pt_regs *regs)
+{
+	union offset_union offset;
+	unsigned long instrptr;
+	int (*handler)(unsigned long addr, u32 instr, struct pt_regs *regs);
+	unsigned int type;
+	u32 instr = 0;
+	u16 tinstr = 0;
+	int isize = 4;
+	int thumb2_32b = 0;
+	int fault;
+
+	instrptr = instruction_pointer(regs);
+
+	if (compat_thumb_mode(regs)) {
+		__le16 __user *ptr = (__le16 __user *)(instrptr & ~1);
+
+		fault = alignment_get_thumb(regs, ptr, &tinstr);
+		if (!fault) {
+			if (IS_T32(tinstr)) {
+				/* Thumb-2 32-bit */
+				u16 tinst2;
+				fault = alignment_get_thumb(regs, ptr + 1, &tinst2);
+				instr = ((u32)tinstr << 16) | tinst2;
+				thumb2_32b = 1;
+			} else {
+				isize = 2;
+				instr = thumb2arm(tinstr);
+			}
+		}
+	} else {
+		fault = alignment_get_arm(regs, (__le32 __user *)instrptr, &instr);
+	}
+
+	if (fault)
+		return 1;
+
+	switch (CODING_BITS(instr)) {
+	case 0x00000000:	/* 3.13.4 load/store instruction extensions */
+		if (LDSTHD_I_BIT(instr))
+			offset.un = (instr & 0xf00) >> 4 | (instr & 15);
+		else
+			offset.un = regs->regs[RM_BITS(instr)];
+
+		if ((instr & 0x001000f0) == 0x000000d0 || /* LDRD */
+		    (instr & 0x001000f0) == 0x000000f0)   /* STRD */
+			handler = do_alignment_ldrdstrd;
+		else
+			return 1;
+		break;
+
+	case 0x08000000:	/* ldm or stm, or thumb-2 32bit instruction */
+		if (thumb2_32b) {
+			offset.un = 0;
+			handler = do_alignment_t32_to_handler(&instr, regs, &offset);
+		} else {
+			offset.un = 0;
+			handler = do_alignment_ldmstm;
+		}
+		break;
+
+	default:
+		return 1;
+	}
+
+	type = handler(addr, instr, regs);
+
+	if (type == TYPE_ERROR || type == TYPE_FAULT)
+		return 1;
+
+	if (type == TYPE_LDST)
+		do_alignment_finish_ldst(addr, instr, regs, offset);
+
+	perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, regs->pc);
+	arm64_skip_faulting_instruction(regs, isize);
+
+	return 0;
+}