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Subject[PATCH AUTOSEL 4.18 051/126] arm64: entry: Allow handling of undefined instructions from EL1
Date
From: Will Deacon <will.deacon@arm.com>

[ Upstream commit 0bf0f444b2c49241b2b39aa3cf210d7c95ef6c34 ]

Rather than panic() when taking an undefined instruction exception from
EL1, allow a hook to be registered in case we want to emulate the
instruction, like we will for the SSBS PSTATE manipulation instructions.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/kernel/entry.S | 2 +-
arch/arm64/kernel/traps.c | 11 +++++++----
2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 28ad8799406f..b0db91eefbde 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -599,7 +599,7 @@ el1_undef:
inherit_daif pstate=x23, tmp=x2
mov x0, sp
bl do_undefinstr
- ASM_BUG()
+ kernel_exit 1
el1_dbg:
/*
* Debug exception handling
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index d399d459397b..9fa3d69cceaa 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -310,10 +310,12 @@ static int call_undef_hook(struct pt_regs *regs)
int (*fn)(struct pt_regs *regs, u32 instr) = NULL;
void __user *pc = (void __user *)instruction_pointer(regs);

- if (!user_mode(regs))
- return 1;
-
- if (compat_thumb_mode(regs)) {
+ if (!user_mode(regs)) {
+ __le32 instr_le;
+ if (probe_kernel_address((__force __le32 *)pc, instr_le))
+ goto exit;
+ instr = le32_to_cpu(instr_le);
+ } else if (compat_thumb_mode(regs)) {
/* 16-bit Thumb instruction */
__le16 instr_le;
if (get_user(instr_le, (__le16 __user *)pc))
@@ -407,6 +409,7 @@ asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
return;

force_signal_inject(SIGILL, ILL_ILLOPC, regs->pc);
+ BUG_ON(!user_mode(regs));
}

void cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused)
--
2.17.1
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