On Wed, 12 Jun 2024 at 13:02, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I'll send out a new version of the arm64 patches with the KCSAN build
> failure fixed (with the simple no-op save/restore functions by making
> KCSAN and SW PAN mutually incompatible), and with the virtual address
> fix you pointed out in the other email.
Actually, unless somebody really wants to see the whole series again,
here's just the diff between the end result of the series.
The actual changes are done in the relevant commits (ie the "asm goto
for get_user()" one for the KCSAN issue, and the "arm64 runtime
constant" commit for the I$ fixup).
Holler if you want to see the full series again.
It might be worth noting that I initially made the arm64 KCSAN support
have a "depend on !ARM64_SW_TTBR0_PAN" condition, but decided that
it's actually better to do it the other way around, and make
ARM64_SW_TTBR0_PAN depend on KCSAN not being enabled.
That way we're basically more eagerly disabling the thing that should
go away, and we're also having the KCSAN code be checked for
allmodconfig builds.
But hey, it's a judgement call.
Linus
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5d91259ee7b5..b6e8920364de 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1649,6 +1649,7 @@ config RODATA_FULL_DEFAULT_ENABLED
config ARM64_SW_TTBR0_PAN
bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
+ depends on !KCSAN
help
Enabling this option prevents the kernel from accessing
user-space memory directly by pointing TTBR0_EL1 to a reserved
diff --git a/arch/arm64/include/asm/runtime-const.h b/arch/arm64/include/asm/runtime-const.h
index 8dc83d48a202..dde4c11ec0d5 100644
--- a/arch/arm64/include/asm/runtime-const.h
+++ b/arch/arm64/include/asm/runtime-const.h
@@ -50,6 +50,12 @@ static inline void __runtime_fixup_16(__le32 *p, unsigned int val)
*p = cpu_to_le32(insn);
}
+static inline void __runtime_fixup_caches(void *where, unsigned int insns)
+{
+ unsigned long va = (unsigned long)where;
+ caches_clean_inval_pou(va, va + 4*insns);
+}
+
static inline void __runtime_fixup_ptr(void *where, unsigned long val)
{
__le32 *p = lm_alias(where);
@@ -57,7 +63,7 @@ static inline void __runtime_fixup_ptr(void *where, unsigned long val)
__runtime_fixup_16(p+1, val >> 16);
__runtime_fixup_16(p+2, val >> 32);
__runtime_fixup_16(p+3, val >> 48);
- caches_clean_inval_pou((unsigned long)p, (unsigned long)(p + 4));
+ __runtime_fixup_caches(where, 4);
}
/* Immediate value is 6 bits starting at bit #16 */
@@ -68,7 +74,7 @@ static inline void __runtime_fixup_shift(void *where, unsigned long val)
insn &= 0xffc0ffff;
insn |= (val & 63) << 16;
*p = cpu_to_le32(insn);
- caches_clean_inval_pou((unsigned long)p, (unsigned long)(p + 1));
+ __runtime_fixup_caches(where, 1);
}
static inline void runtime_const_fixup(void (*fn)(void *, unsigned long),
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 37abd893c6ee..1f21190d4db5 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -424,6 +424,14 @@ static __must_check __always_inline bool user_access_begin(const void __user *pt
#define unsafe_get_user(x, ptr, label) \
__raw_get_mem("ldtr", x, uaccess_mask_ptr(ptr), label, U)
+/*
+ * KCSAN uses these to save and restore ttbr state.
+ * We do not support KCSAN with ARM64_SW_TTBR0_PAN, so
+ * they are no-ops.
+ */
+static inline unsigned long user_access_save(void) { return 0; }
+static inline void user_access_restore(unsigned long enabled) { }
+
/*
* We want the unsafe accessors to always be inlined and use
* the error labels - thus the macro games.
