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authorMark Rutland <mark.rutland@arm.com>2020-11-13 12:49:21 +0000
committerCatalin Marinas <catalin.marinas@arm.com>2020-12-02 19:44:02 +0000
commitf80d034086d5bfcfd3bf4ab6f52b2df78c3ad2fa (patch)
tree73dbd05a9baf36f1d204f5be7b989e01c9d26ae1
parente35123d83ee35c31f64ecfbdfabbe5142d3025b8 (diff)
downloadlinux-f80d034086d5bfcfd3bf4ab6f52b2df78c3ad2fa.tar.bz2
arm64: ensure ERET from kthread is illegal
For consistency, all tasks have a pt_regs reserved at the highest portion of their task stack. Among other things, this ensures that a task's SP is always pointing within its stack rather than pointing immediately past the end. While it is never legitimate to ERET from a kthread, we take pains to initialize pt_regs for kthreads as if this were legitimate. As this is never legitimate, the effects of an erroneous return are rarely tested. Let's simplify things by initializing a kthread's pt_regs such that an ERET is caught as an illegal exception return, and removing the explicit initialization of other exception context. Note that as spectre_v4_enable_task_mitigation() only manipulates the PSTATE within the unused regs this is safe to remove. As user tasks will have their exception context initialized via start_thread() or start_compat_thread(), this should only impact cases where something has gone very wrong and we'd like that to be clearly indicated. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: James Morse <james.morse@arm.com> Cc: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20201113124937.20574-2-mark.rutland@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
-rw-r--r--arch/arm64/kernel/process.c17
1 files changed, 8 insertions, 9 deletions
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 4784011cecac..855137daafbf 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -422,16 +422,15 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
if (clone_flags & CLONE_SETTLS)
p->thread.uw.tp_value = tls;
} else {
+ /*
+ * A kthread has no context to ERET to, so ensure any buggy
+ * ERET is treated as an illegal exception return.
+ *
+ * When a user task is created from a kthread, childregs will
+ * be initialized by start_thread() or start_compat_thread().
+ */
memset(childregs, 0, sizeof(struct pt_regs));
- childregs->pstate = PSR_MODE_EL1h;
- if (IS_ENABLED(CONFIG_ARM64_UAO) &&
- cpus_have_const_cap(ARM64_HAS_UAO))
- childregs->pstate |= PSR_UAO_BIT;
-
- spectre_v4_enable_task_mitigation(p);
-
- if (system_uses_irq_prio_masking())
- childregs->pmr_save = GIC_PRIO_IRQON;
+ childregs->pstate = PSR_MODE_EL1h | PSR_IL_BIT;
p->thread.cpu_context.x19 = stack_start;
p->thread.cpu_context.x20 = stk_sz;