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Date: Tue, 19 Mar 2024 14:58:33 -0700
From: Samuel Holland <samuel.holland@...ive.com>
To: Palmer Dabbelt <palmer@...belt.com>,
linux-riscv@...ts.infradead.org
Cc: devicetree@...r.kernel.org,
Catalin Marinas <catalin.marinas@....com>,
linux-kernel@...r.kernel.org,
tech-j-ext@...ts.risc-v.org,
Conor Dooley <conor@...nel.org>,
kasan-dev@...glegroups.com,
Evgenii Stepanov <eugenis@...gle.com>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Rob Herring <robh+dt@...nel.org>,
Samuel Holland <samuel.holland@...ive.com>,
Albert Ou <aou@...s.berkeley.edu>,
Greentime Hu <greentime.hu@...ive.com>
Subject: [RFC PATCH 7/9] riscv: Add support for the tagged address ABI
When pointer masking is enabled for userspace, the kernel can accept
tagged pointers as arguments to some system calls. Allow this by
untagging the pointers in access_ok() and the uaccess routines. The
software untagging in the uaccess routines is required because U-mode
and S-mode have entirely separate pointer masking configurations.
Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---
arch/riscv/include/asm/processor.h | 1 +
arch/riscv/include/asm/uaccess.h | 40 +++++++++++++++++++++---
arch/riscv/kernel/process.c | 49 +++++++++++++++++++++++++++++-
3 files changed, 84 insertions(+), 6 deletions(-)
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 64b34e839802..cdc8569b2118 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -124,6 +124,7 @@ struct thread_struct {
struct __riscv_v_ext_state vstate;
unsigned long align_ctl;
struct __riscv_v_ext_state kernel_vstate;
+ u8 pmlen;
};
/* Whitelist the fstate from the task_struct for hardened usercopy */
diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
index ec0cab9fbddd..ed282dcf9a6d 100644
--- a/arch/riscv/include/asm/uaccess.h
+++ b/arch/riscv/include/asm/uaccess.h
@@ -9,8 +9,38 @@
#define _ASM_RISCV_UACCESS_H
#include <asm/asm-extable.h>
+#include <asm/cpufeature.h>
#include <asm/pgtable.h> /* for TASK_SIZE */
+#ifdef CONFIG_RISCV_ISA_POINTER_MASKING
+static inline unsigned long __untagged_addr(unsigned long addr)
+{
+ if (riscv_has_extension_unlikely(RISCV_ISA_EXT_SxNPM)) {
+ u8 shift = current->thread.pmlen;
+
+ /*
+ * Virtual addresses are sign-extended, while
+ * physical addresses are zero-extended.
+ */
+ if (IS_ENABLED(CONFIG_MMU))
+ return (long)(addr << shift) >> shift;
+ else
+ return (addr << shift) >> shift;
+ }
+
+ return addr;
+}
+
+#define untagged_addr(addr) ({ \
+ unsigned long __addr = (__force unsigned long)(addr); \
+ (__force __typeof__(addr))__untagged_addr(__addr); \
+})
+
+#define access_ok(addr, size) likely(__access_ok(untagged_addr(addr), size))
+#else
+#define untagged_addr(addr) addr
+#endif
+
/*
* User space memory access functions
*/
@@ -130,7 +160,7 @@ do { \
*/
#define __get_user(x, ptr) \
({ \
- const __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \
+ const __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
long __gu_err = 0; \
\
__chk_user_ptr(__gu_ptr); \
@@ -246,7 +276,7 @@ do { \
*/
#define __put_user(x, ptr) \
({ \
- __typeof__(*(ptr)) __user *__gu_ptr = (ptr); \
+ __typeof__(*(ptr)) __user *__gu_ptr = untagged_addr(ptr); \
__typeof__(*__gu_ptr) __val = (x); \
long __pu_err = 0; \
\
@@ -293,13 +323,13 @@ unsigned long __must_check __asm_copy_from_user(void *to,
static inline unsigned long
raw_copy_from_user(void *to, const void __user *from, unsigned long n)
{
- return __asm_copy_from_user(to, from, n);
+ return __asm_copy_from_user(to, untagged_addr(from), n);
}
static inline unsigned long
raw_copy_to_user(void __user *to, const void *from, unsigned long n)
{
- return __asm_copy_to_user(to, from, n);
+ return __asm_copy_to_user(untagged_addr(to), from, n);
}
extern long strncpy_from_user(char *dest, const char __user *src, long count);
@@ -314,7 +344,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
{
might_fault();
return access_ok(to, n) ?
- __clear_user(to, n) : n;
+ __clear_user(untagged_addr(to), n) : n;
}
#define __get_kernel_nofault(dst, src, type, err_label) \
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 3578e75f4aa4..36129040b7bd 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -162,6 +162,7 @@ static void flush_tagged_addr_state(void)
return;
current->thread.envcfg &= ~ENVCFG_PMM;
+ current->thread.pmlen = 0;
sync_envcfg(current);
#endif
@@ -255,9 +256,14 @@ void __init arch_task_cache_init(void)
static bool have_user_pmlen_7;
static bool have_user_pmlen_16;
+/*
+ * Control the relaxed ABI allowing tagged user addresses into the kernel.
+ */
+static unsigned int tagged_addr_disabled;
+
long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
{
- unsigned long valid_mask = PR_PMLEN_MASK;
+ unsigned long valid_mask = PR_PMLEN_MASK | PR_TAGGED_ADDR_ENABLE;
struct thread_info *ti = task_thread_info(task);
u8 pmlen;
@@ -288,12 +294,25 @@ long set_tagged_addr_ctrl(struct task_struct *task, unsigned long arg)
return -EINVAL;
}
+ /*
+ * Do not allow the enabling of the tagged address ABI if globally
+ * disabled via sysctl abi.tagged_addr_disabled, if pointer masking
+ * is disabled for userspace.
+ */
+ if (arg & PR_TAGGED_ADDR_ENABLE && (tagged_addr_disabled || !pmlen))
+ return -EINVAL;
+
task->thread.envcfg &= ~ENVCFG_PMM;
if (pmlen == 7)
task->thread.envcfg |= ENVCFG_PMM_PMLEN_7;
else if (pmlen == 16)
task->thread.envcfg |= ENVCFG_PMM_PMLEN_16;
+ if (arg & PR_TAGGED_ADDR_ENABLE)
+ task->thread.pmlen = pmlen;
+ else
+ task->thread.pmlen = 0;
+
if (task == current)
sync_envcfg(current);
@@ -308,6 +327,13 @@ long get_tagged_addr_ctrl(struct task_struct *task)
if (is_compat_thread(ti))
return -EINVAL;
+ if (task->thread.pmlen)
+ ret = PR_TAGGED_ADDR_ENABLE;
+
+ /*
+ * The task's pmlen is only set if the tagged address ABI is enabled,
+ * so the effective PMLEN must be extracted from envcfg.PMM.
+ */
switch (task->thread.envcfg & ENVCFG_PMM) {
case ENVCFG_PMM_PMLEN_7:
ret |= FIELD_PREP(PR_PMLEN_MASK, 7);
@@ -326,6 +352,24 @@ static bool try_to_set_pmm(unsigned long value)
return (csr_read_clear(CSR_ENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
}
+/*
+ * Global sysctl to disable the tagged user addresses support. This control
+ * only prevents the tagged address ABI enabling via prctl() and does not
+ * disable it for tasks that already opted in to the relaxed ABI.
+ */
+
+static struct ctl_table tagged_addr_sysctl_table[] = {
+ {
+ .procname = "tagged_addr_disabled",
+ .mode = 0644,
+ .data = &tagged_addr_disabled,
+ .maxlen = sizeof(int),
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE,
+ },
+};
+
static int __init tagged_addr_init(void)
{
if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SxNPM))
@@ -339,6 +383,9 @@ static int __init tagged_addr_init(void)
have_user_pmlen_7 = try_to_set_pmm(ENVCFG_PMM_PMLEN_7);
have_user_pmlen_16 = try_to_set_pmm(ENVCFG_PMM_PMLEN_16);
+ if (!register_sysctl("abi", tagged_addr_sysctl_table))
+ return -EINVAL;
+
return 0;
}
core_initcall(tagged_addr_init);
--
2.43.1
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