[PATCH 4/7] arm64: probes: Add GCS support to bl/blr/ret

[Jeremy Linton]

The arm64 probe simulation doesn't currently have logic in place
to deal with GCS and this results in core dumps if probes are inserted
at control flow locations. Fix-up bl, blr and ret to manipulate the
shadow stack as needed.

Signed-off-by: Jeremy Linton <jeremy.lin...@arm.com>
---
 arch/arm64/kernel/probes/simulate-insn.c | 28 ++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/probes/simulate-insn.c 
b/arch/arm64/kernel/probes/simulate-insn.c
index 09a0b36122d0..1fc9bb69b1eb 100644
--- a/arch/arm64/kernel/probes/simulate-insn.c
+++ b/arch/arm64/kernel/probes/simulate-insn.c
@@ -13,6 +13,7 @@
 #include <asm/traps.h>
 
 #include "simulate-insn.h"
+#include "asm/gcs.h"
 
 #define bbl_displacement(insn)         \
        sign_extend32(((insn) & 0x3ffffff) << 2, 27)
@@ -49,6 +50,18 @@ static inline u32 get_w_reg(struct pt_regs *regs, int reg)
        return lower_32_bits(pt_regs_read_reg(regs, reg));
 }
 
+static inline void update_lr(struct pt_regs *regs, long addr)
+{
+       int err = 0;
+
+       if (user_mode(regs) && task_gcs_el0_enabled(current)) {
+               push_user_gcs(addr + 4,  &err);
+               if (err)
+                       force_sig(SIGSEGV);
+       }
+       procedure_link_pointer_set(regs, addr + 4);
+}
+
 static bool __kprobes check_cbz(u32 opcode, struct pt_regs *regs)
 {
        int xn = opcode & 0x1f;
@@ -107,9 +120,8 @@ simulate_b_bl(u32 opcode, long addr, struct pt_regs *regs)
 {
        int disp = bbl_displacement(opcode);
 
-       /* Link register is x30 */
        if (opcode & (1 << 31))
-               set_x_reg(regs, 30, addr + 4);
+               update_lr(regs, addr);
 
        instruction_pointer_set(regs, addr + disp);
 }
@@ -133,17 +145,25 @@ simulate_br_blr(u32 opcode, long addr, struct pt_regs 
*regs)
        /* update pc first in case we're doing a "blr lr" */
        instruction_pointer_set(regs, get_x_reg(regs, xn));
 
-       /* Link register is x30 */
        if (((opcode >> 21) & 0x3) == 1)
-               set_x_reg(regs, 30, addr + 4);
+               update_lr(regs, addr);
 }
 
 void __kprobes
 simulate_ret(u32 opcode, long addr, struct pt_regs *regs)
 {
+       u64 ret_addr;
+       int err = 0;
        int xn = (opcode >> 5) & 0x1f;
 
        instruction_pointer_set(regs, get_x_reg(regs, xn));
+
+       if (user_mode(regs) && task_gcs_el0_enabled(current)) {
+               ret_addr = pop_user_gcs(&err);
+               if (err || ret_addr != procedure_link_pointer(regs))
+                       force_sig(SIGSEGV);
+       }
+
 }
 
 void __kprobes
-- 
2.48.1