linux-kernel - [PATCH] riscv: process: Fix kernel gp leakage

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Message-Id: <20240327061258.2370291-1-sorear@fastmail.com>
Date: Wed, 27 Mar 2024 02:12:58 -0400
From: Stefan O'Rear <sorear@...tmail.com>
To: linux-riscv@...ts.infradead.org,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	linux-kernel@...r.kernel.org
Cc: Stefan O'Rear <sorear@...tmail.com>
Subject: [PATCH] riscv: process: Fix kernel gp leakage

childregs represents the registers which are active for the new thread
in user context. For a kernel thread, childregs->gp is never used since
the kernel gp is not touched by switch_to. For a user mode helper, the
gp value can be observed in user space after execve or possibly by other
means.

Fixes: 7db91e57a0ac ("RISC-V: Task implementation")
Signed-off-by: Stefan O'Rear <sorear@...tmail.com>
---
 arch/riscv/kernel/process.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 92922dbd5b5c..51042f48da17 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -27,8 +27,6 @@
 #include <asm/vector.h>
 #include <asm/cpufeature.h>
 
-register unsigned long gp_in_global __asm__("gp");
-
 #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
 #include <linux/stackprotector.h>
 unsigned long __stack_chk_guard __read_mostly;
@@ -207,7 +205,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	if (unlikely(args->fn)) {
 		/* Kernel thread */
 		memset(childregs, 0, sizeof(struct pt_regs));
-		childregs->gp = gp_in_global;
 		/* Supervisor/Machine, irqs on: */
 		childregs->status = SR_PP | SR_PIE;
 
-- 
2.40.1