x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 411 insertions, 0 deletions

diff --git a/arch/arm64/tools/gen-sysreg.awk b/arch/arm64/tools/gen-sysreg.awk
new file mode 100755
index 000000000..53844f5c5
--- /dev/null
+++ b/arch/arm64/tools/gen-sysreg.awk
@@ -0,0 +1,411 @@
+#!/bin/awk -f
+# SPDX-License-Identifier: GPL-2.0
+# gen-sysreg.awk: arm64 sysreg header generator
+#
+# Usage: awk -f gen-sysreg.awk sysregs.txt
+
+function block_current() {
+	return __current_block[__current_block_depth];
+}
+
+# Log an error and terminate
+function fatal(msg) {
+	print "Error at " NR ": " msg > "/dev/stderr"
+
+	printf "Current block nesting:"
+
+	for (i = 0; i <= __current_block_depth; i++) {
+		printf " " __current_block[i]
+	}
+	printf "\n"
+
+	exit 1
+}
+
+# Enter a new block, setting the active block to @block
+function block_push(block) {
+	__current_block[++__current_block_depth] = block
+}
+
+# Exit a block, setting the active block to the parent block
+function block_pop() {
+	if (__current_block_depth == 0)
+		fatal("error: block_pop() in root block")
+
+	__current_block_depth--;
+}
+
+# Sanity check the number of records for a field makes sense. If not, produce
+# an error and terminate.
+function expect_fields(nf) {
+	if (NF != nf)
+		fatal(NF " fields found where " nf " expected")
+}
+
+# Print a CPP macro definition, padded with spaces so that the macro bodies
+# line up in a column
+function define(prefix, name, val) {
+	printf "%-56s%s\n", "#define " prefix name, val
+}
+
+# Same as above, but without a prefix
+function define_reg(name, val) {
+	define(null, name, val)
+}
+
+# Print standard BITMASK/SHIFT/WIDTH CPP definitions for a field
+function define_field(prefix, reg, field, msb, lsb) {
+	define(prefix, reg "_" field, "GENMASK(" msb ", " lsb ")")
+	define(prefix, reg "_" field "_MASK", "GENMASK(" msb ", " lsb ")")
+	define(prefix, reg "_" field "_SHIFT", lsb)
+	define(prefix, reg "_" field "_WIDTH", msb - lsb + 1)
+}
+
+# Print a field _SIGNED definition for a field
+function define_field_sign(prefix, reg, field, sign) {
+	define(prefix, reg "_" field "_SIGNED", sign)
+}
+
+# Print the Res0, Res1, Unkn masks
+function define_resx_unkn(prefix, reg, res0, res1, unkn) {
+	if (res0 != null)
+		define(prefix, reg "_RES0", "(" res0 ")")
+	if (res1 != null)
+		define(prefix, reg "_RES1", "(" res1 ")")
+	if (unkn != null)
+		define(prefix, reg "_UNKN", "(" unkn ")")
+	if (res0 != null || res1 != null || unkn != null)
+		print ""
+}
+
+# Parse a "<msb>[:<lsb>]" string into the global variables @msb and @lsb
+function parse_bitdef(reg, field, bitdef, _bits)
+{
+	if (bitdef ~ /^[0-9]+$/) {
+		msb = bitdef
+		lsb = bitdef
+	} else if (split(bitdef, _bits, ":") == 2) {
+		msb = _bits[1]
+		lsb = _bits[2]
+	} else {
+		fatal("invalid bit-range definition '" bitdef "'")
+	}
+
+
+	if (msb != next_bit)
+		fatal(reg "." field " starts at " msb " not " next_bit)
+	if (63 < msb || msb < 0)
+		fatal(reg "." field " invalid high bit in '" bitdef "'")
+	if (63 < lsb || lsb < 0)
+		fatal(reg "." field " invalid low bit in '" bitdef "'")
+	if (msb < lsb)
+		fatal(reg "." field " invalid bit-range '" bitdef "'")
+	if (low > high)
+		fatal(reg "." field " has invalid range " high "-" low)
+
+	next_bit = lsb - 1
+}
+
+BEGIN {
+	print "#ifndef __ASM_SYSREG_DEFS_H"
+	print "#define __ASM_SYSREG_DEFS_H"
+	print ""
+	print "/* Generated file - do not edit */"
+	print ""
+
+	__current_block_depth = 0
+	__current_block[__current_block_depth] = "Root"
+}
+
+END {
+	if (__current_block_depth != 0)
+		fatal("Missing terminator for " block_current() " block")
+
+	print "#endif /* __ASM_SYSREG_DEFS_H */"
+}
+
+# skip blank lines and comment lines
+/^$/ { next }
+/^[\t ]*#/ { next }
+
+$1 == "SysregFields" && block_current() == "Root" {
+	block_push("SysregFields")
+
+	expect_fields(2)
+
+	reg = $2
+
+	res0 = "UL(0)"
+	res1 = "UL(0)"
+	unkn = "UL(0)"
+
+	if (reg in defined_fields)
+		fatal("Duplicate SysregFields definition for " reg)
+	defined_fields[reg] = 1
+
+	next_bit = 63
+
+	delete seen_prefixes
+
+	next
+}
+
+$1 == "EndSysregFields" && block_current() == "SysregFields" {
+	expect_fields(1)
+	if (next_bit >= 0)
+		fatal("Unspecified bits in " reg)
+
+	define_resx_unkn(prefix, reg, res0, res1, unkn)
+
+	reg = null
+	res0 = null
+	res1 = null
+	unkn = null
+
+	block_pop()
+	next
+}
+
+$1 == "Sysreg" && block_current() == "Root" {
+	block_push("Sysreg")
+
+	expect_fields(7)
+
+	reg = $2
+	op0 = $3
+	op1 = $4
+	crn = $5
+	crm = $6
+	op2 = $7
+
+	res0 = "UL(0)"
+	res1 = "UL(0)"
+	unkn = "UL(0)"
+
+	if (reg in defined_regs)
+		fatal("Duplicate Sysreg definition for " reg)
+	defined_regs[reg] = 1
+
+	define_reg("REG_" reg, "S" op0 "_" op1 "_C" crn "_C" crm "_" op2)
+	define_reg("SYS_" reg, "sys_reg(" op0 ", " op1 ", " crn ", " crm ", " op2 ")")
+
+	define_reg("SYS_" reg "_Op0", op0)
+	define_reg("SYS_" reg "_Op1", op1)
+	define_reg("SYS_" reg "_CRn", crn)
+	define_reg("SYS_" reg "_CRm", crm)
+	define_reg("SYS_" reg "_Op2", op2)
+
+	print ""
+
+	prefix = null
+	next_bit = 63
+
+	delete seen_prefixes
+
+	next
+}
+
+$1 == "EndSysreg" && block_current() == "Sysreg" {
+	expect_fields(1)
+	if (next_bit >= 0)
+		fatal("Unspecified bits in " reg)
+
+	define_resx_unkn(prefix, reg, res0, res1, unkn)
+
+	reg = null
+	op0 = null
+	op1 = null
+	crn = null
+	crm = null
+	op2 = null
+	res0 = null
+	res1 = null
+	unkn = null
+	prefix = null
+
+	block_pop()
+	next
+}
+
+# Currently this is effectivey a comment, in future we may want to emit
+# defines for the fields. We do emit RESx and UNKN values in any case.
+($1 == "Fields" || $1 == "Mapping") && block_current() == "Sysreg" {
+	expect_fields(2)
+
+	if (next_bit != 63)
+		fatal("Some fields already defined for " reg)
+
+	print "/* For " reg " fields see " $2 " */"
+	print ""
+
+	next_bit = -1
+	res0 = $2 "_RES0"
+	res1 = $2 "_RES1"
+	unkn = $2 "_UNKN"
+
+	next
+}
+
+$1 == "Res0" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(2)
+	parse_bitdef(reg, "RES0", $2)
+	field = "RES0_" msb "_" lsb
+
+	res0 = res0 " | GENMASK_ULL(" msb ", " lsb ")"
+
+	next
+}
+
+$1 == "Res1" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(2)
+	parse_bitdef(reg, "RES1", $2)
+	field = "RES1_" msb "_" lsb
+
+	res1 = res1 " | GENMASK_ULL(" msb ", " lsb ")"
+
+	next
+}
+
+$1 == "Unkn" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(2)
+	parse_bitdef(reg, "UNKN", $2)
+	field = "UNKN_" msb "_" lsb
+
+	unkn = unkn " | GENMASK_ULL(" msb ", " lsb ")"
+
+	next
+}
+
+$1 == "Field" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(3)
+	field = $3
+	parse_bitdef(reg, field, $2)
+
+	define_field(prefix, reg, field, msb, lsb)
+	print ""
+
+	next
+}
+
+$1 == "Raz" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	expect_fields(2)
+	parse_bitdef(reg, field, $2)
+
+	next
+}
+
+$1 == "SignedEnum" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	block_push("Enum")
+
+	expect_fields(3)
+	field = $3
+	parse_bitdef(reg, field, $2)
+
+	define_field(prefix, reg, field, msb, lsb)
+	define_field_sign(prefix, reg, field, "true")
+
+	delete seen_enum_vals
+
+	next
+}
+
+$1 == "UnsignedEnum" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	block_push("Enum")
+
+	expect_fields(3)
+	field = $3
+	parse_bitdef(reg, field, $2)
+
+	define_field(prefix, reg, field, msb, lsb)
+	define_field_sign(prefix, reg, field, "false")
+
+	delete seen_enum_vals
+
+	next
+}
+
+$1 == "Enum" && (block_current() == "Sysreg" || block_current() == "SysregFields" || block_current() == "Prefix") {
+	block_push("Enum")
+
+	expect_fields(3)
+	field = $3
+	parse_bitdef(reg, field, $2)
+
+	define_field(prefix, reg, field, msb, lsb)
+
+	delete seen_enum_vals
+
+	next
+}
+
+$1 == "EndEnum" && block_current() == "Enum" {
+	expect_fields(1)
+
+	field = null
+	msb = null
+	lsb = null
+	print ""
+
+	delete seen_enum_vals
+
+	block_pop()
+	next
+}
+
+/0b[01]+/ && block_current() == "Enum" {
+	expect_fields(2)
+	val = $1
+	name = $2
+
+	if (val in seen_enum_vals)
+		fatal("Duplicate Enum value " val " for " name)
+	seen_enum_vals[val] = 1
+
+	define(prefix, reg "_" field "_" name, "UL(" val ")")
+	next
+}
+
+$1 == "Prefix" && (block_current() == "Sysreg" || block_current() == "SysregFields") {
+	block_push("Prefix")
+
+	expect_fields(2)
+
+	if (next_bit < 63)
+		fatal("Prefixed fields must precede non-prefixed fields (" reg ")")
+
+	prefix = $2 "_"
+
+	if (prefix in seen_prefixes)
+		fatal("Duplicate prefix " prefix " for " reg)
+	seen_prefixes[prefix] = 1
+
+	res0 = "UL(0)"
+	res1 = "UL(0)"
+	unkn = "UL(0)"
+	next_bit = 63
+
+	next
+}
+
+$1 == "EndPrefix" && block_current() == "Prefix" {
+	expect_fields(1)
+	if (next_bit >= 0)
+		fatal("Unspecified bits in prefix " prefix " for " reg)
+
+	define_resx_unkn(prefix, reg, res0, res1, unkn)
+
+	prefix = null
+	res0 = "UL(0)"
+	res1 = "UL(0)"
+	unkn = "UL(0)"
+	next_bit = 63
+
+	block_pop()
+
+	next
+}
+
+# Any lines not handled by previous rules are unexpected
+{
+	fatal("unhandled statement")
+}