[PATCH v8 1/6] arm64: kprobe: add checks for ARMv8.3-PAuth combined instructions

Amit Daniel Kachhap
2020-09-14T08:38:33Z

Currently the ARMv8.3-PAuth combined branch instructions (braa, retaa
etc.) are not simulated for out-of-line execution with a handler. Hence the
uprobe of such instructions leads to kernel warnings in a loop as they are
not explicitly checked and fall into INSN_GOOD categories. Other combined
instructions like LDRAA and LDRBB can be probed.

The issue of the combined branch instructions is fixed by adding
group definitions of all such instructions and rejecting their probes.
The instruction groups added are br_auth(braa, brab, braaz and brabz),
blr_auth(blraa, blrab, blraaz and blrabz), ret_auth(retaa and retab) and
eret_auth(eretaa and eretab).

Warning log:
WARNING: CPU: 0 PID: 156 at arch/arm64/kernel/probes/uprobes.c:182 uprobe_single_step_handler+0x34/0x50
Modules linked in:
CPU: 0 PID: 156 Comm: func Not tainted 5.9.0-rc3 #188
Hardware name: Foundation-v8A (DT)
pstate: 804003c9 (Nzcv DAIF +PAN -UAO BTYPE=--)
pc : uprobe_single_step_handler+0x34/0x50
lr : single_step_handler+0x70/0xf8
sp : ffff800012af3e30
x29: ffff800012af3e30 x28: ffff000878723b00
x27: 0000000000000000 x26: 0000000000000000
x25: 0000000000000000 x24: 0000000000000000
x23: 0000000060001000 x22: 00000000cb000022
x21: ffff800012065ce8 x20: ffff800012af3ec0
x19: ffff800012068d50 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000
x15: 0000000000000000 x14: 0000000000000000
x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000
x9 : ffff800010085c90 x8 : 0000000000000000
x7 : 0000000000000000 x6 : ffff80001205a9c8
x5 : ffff80001205a000 x4 : ffff80001233db80
x3 : ffff8000100a7a60 x2 : 0020000000000003
x1 : 0000fffffffff008 x0 : ffff800012af3ec0
Call trace:
uprobe_single_step_handler+0x34/0x50
single_step_handler+0x70/0xf8
do_debug_exception+0xb8/0x130
el0_sync_handler+0x138/0x1b8
el0_sync+0x158/0x180

Fixes: 74afda4016a7 ("arm64: compile the kernel with ptrauth return address signing")
Fixes: 04ca3204fa09 ("arm64: enable pointer authentication")
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
---
arch/arm64/include/asm/insn.h | 4 ++++
arch/arm64/kernel/insn.c | 5 ++++-
arch/arm64/kernel/probes/decode-insn.c | 3 ++-
3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index 0bc46149e491..4b39293d0f72 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -359,9 +359,13 @@ __AARCH64_INSN_FUNCS(brk, 0xFFE0001F, 0xD4200000)
__AARCH64_INSN_FUNCS(exception, 0xFF000000, 0xD4000000)
__AARCH64_INSN_FUNCS(hint, 0xFFFFF01F, 0xD503201F)
__AARCH64_INSN_FUNCS(br, 0xFFFFFC1F, 0xD61F0000)
+__AARCH64_INSN_FUNCS(br_auth, 0xFEFFF800, 0xD61F0800)
__AARCH64_INSN_FUNCS(blr, 0xFFFFFC1F, 0xD63F0000)
+__AARCH64_INSN_FUNCS(blr_auth, 0xFEFFF800, 0xD63F0800)
__AARCH64_INSN_FUNCS(ret, 0xFFFFFC1F, 0xD65F0000)
+__AARCH64_INSN_FUNCS(ret_auth, 0xFFFFFBFF, 0xD65F0BFF)
__AARCH64_INSN_FUNCS(eret, 0xFFFFFFFF, 0xD69F03E0)
+__AARCH64_INSN_FUNCS(eret_auth, 0xFFFFFBFF, 0xD69F0BFF)
__AARCH64_INSN_FUNCS(mrs, 0xFFF00000, 0xD5300000)
__AARCH64_INSN_FUNCS(msr_imm, 0xFFF8F01F, 0xD500401F)
__AARCH64_INSN_FUNCS(msr_reg, 0xFFF00000, 0xD5100000)
diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index a107375005bc..ccc8c9e22b25 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -176,7 +176,7 @@ bool __kprobes aarch64_insn_uses_literal(u32 insn)

bool __kprobes aarch64_insn_is_branch(u32 insn)
{
- /* b, bl, cb*, tb*, b.cond, br, blr */
+ /* b, bl, cb*, tb*, ret*, b.cond, br*, blr* */

return aarch64_insn_is_b(insn) ||
aarch64_insn_is_bl(insn) ||
@@ -185,8 +185,11 @@ bool __kprobes aarch64_insn_is_branch(u32 insn)
aarch64_insn_is_tbz(insn) ||
aarch64_insn_is_tbnz(insn) ||
aarch64_insn_is_ret(insn) ||
+ aarch64_insn_is_ret_auth(insn) ||
aarch64_insn_is_br(insn) ||
+ aarch64_insn_is_br_auth(insn) ||
aarch64_insn_is_blr(insn) ||
+ aarch64_insn_is_blr_auth(insn) ||
aarch64_insn_is_bcond(insn);
}

diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c
index 263d5fba4c8a..c541fb48886e 100644
--- a/arch/arm64/kernel/probes/decode-insn.c
+++ b/arch/arm64/kernel/probes/decode-insn.c
@@ -29,7 +29,8 @@ static bool __kprobes aarch64_insn_is_steppable(u32 insn)
aarch64_insn_is_msr_imm(insn) ||
aarch64_insn_is_msr_reg(insn) ||
aarch64_insn_is_exception(insn) ||
- aarch64_insn_is_eret(insn))
+ aarch64_insn_is_eret(insn) ||
+ aarch64_insn_is_eret_auth(insn))
return false;

/*