Re: [PATCH v2 2/2] arm64: uaccess: Implement unsafe accessors

On 12/06/2018 06:25 PM, Catalin Marinas wrote:

On Mon, Dec 03, 2018 at 01:55:18PM +0000, Julien Thierry wrote:

quoted

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 07c3408..cabfcae 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h

@@ -233,6 +233,23 @@ static inline void uaccess_enable_not_uao(void)
  	__uaccess_enable(ARM64_ALT_PAN_NOT_UAO);
  }
  
+#define unsafe_user_region_active	uaccess_region_active
+static inline bool uaccess_region_active(void)
+{
+	if (system_uses_ttbr0_pan()) {
+		u64 ttbr;
+
+		ttbr = read_sysreg(ttbr1_el1);
+		return ttbr & TTBR_ASID_MASK;

Nitpick: could write this in 1-2 lines.

True, I can do that in 1 line.

quoted

+	} else if (cpus_have_const_cap(ARM64_ALT_PAN_NOT_UAO)) {
+		return (read_sysreg(sctlr_el1) & SCTLR_EL1_SPAN) ?
+				false :
+				!read_sysreg_s(SYS_PSTATE_PAN);
+	}

ARM64_ALT_PAN_NOT_UAO implies ARM64_HAS_PAN which implies SCTLR_EL1.SPAN
is 0 at run-time. Is this to cope with the case of being called prior to
cpu_enable_pan()?

Yes, the issue I can into is that for cpufeatures, .cpu_enable() callbacks are called inside stop_machine() which obviously might_sleep and so attempts to check whether user_access is on. But for features that get enabled before PAN, the PAN bit will be set.

Thanks,

Julien

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