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Subject[PATCH] riscv: process: Fix kernel gp leakage
Date
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@fastmail.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

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