[PATCH 6.18 633/752] arm64: poe: fix stale POR_EL0 values for ptrace

Sasha Levin
2026-02-28T17:57:26Z

From: Joey Gouly <joey.gouly@arm.com>

[ Upstream commit 1f3b950492db411e6c30ee0076b61ef2694c100a ]

If a process wrote to POR_EL0 and then crashed before a context switch
happened, the coredump would contain an incorrect value for POR_EL0.

The value read in poe_get() would be a stale value left in thread.por_el0. Fix
this by reading the value from the system register, if the target thread is the
current thread.

This matches what gcs/fpsimd do.

Fixes: 175198199262 ("arm64/ptrace: add support for FEAT_POE")
Reported-by: David Spickett <david.spickett@arm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/kernel/ptrace.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index fd1ba43f2005a..2e9ce5a45ed2d 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1458,6 +1458,9 @@ static int poe_get(struct task_struct *target,
if (!system_supports_poe())
return -EINVAL;

+ if (target == current)
+ current->thread.por_el0 = read_sysreg_s(SYS_POR_EL0);
+
return membuf_write(&to, &target->thread.por_el0,
sizeof(target->thread.por_el0));
}
--
2.51.0