[PATCHv3 06/17] arm64: sdei: move uaccess logic to arch/arm64/

Mark Rutland
2020-10-26T13:34:59Z

The SDEI support code is split across arch/arm64/ and drivers/firmware/,
largley this is split so that the arch-specific portions are under
arch/arm64, and the management logic is under drivers/firmware/.
However, exception entry fixups are currently under drivers/firmware.

Let's move the exception entry fixups under arch/arm64/. This
de-clutters the management logic, and puts all the arch-specific
portions in one place. Doing this also allows the fixups to be applied
earlier, so things like PAN and UAO will be in a known good state before
we run other logic. This will also make subsequent refactoring easier.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
---
arch/arm64/kernel/sdei.c | 18 ++++++++++++------
drivers/firmware/arm_sdei.c | 14 --------------
2 files changed, 12 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/kernel/sdei.c b/arch/arm64/kernel/sdei.c
index 7689f2031c0c4..4a5f24602aa0c 100644
--- a/arch/arm64/kernel/sdei.c
+++ b/arch/arm64/kernel/sdei.c
@@ -178,12 +178,6 @@ static __kprobes unsigned long _sdei_handler(struct pt_regs *regs,
sdei_api_event_context(i, &regs->regs[i]);
}

- /*
- * We didn't take an exception to get here, set PAN. UAO will be cleared
- * by sdei_event_handler()s force_uaccess_begin() call.
- */
- __uaccess_enable_hw_pan();
-
err = sdei_event_handler(regs, arg);
if (err)
return SDEI_EV_FAILED;
@@ -227,6 +221,16 @@ asmlinkage __kprobes notrace unsigned long
__sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)
{
unsigned long ret;
+ mm_segment_t orig_addr_limit;
+
+ /*
+ * We didn't take an exception to get here, so the HW hasn't set PAN or
+ * cleared UAO, and the exception entry code hasn't reset addr_limit.
+ * Set PAN, then use force_uaccess_begin() to clear UAO and reset
+ * addr_limit.
+ */
+ __uaccess_enable_hw_pan();
+ orig_addr_limit = force_uaccess_begin();

nmi_enter();

@@ -234,5 +238,7 @@ __sdei_handler(struct pt_regs *regs, struct sdei_registered_event *arg)

nmi_exit();

+ force_uaccess_end(orig_addr_limit);
+
return ret;
}
diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
index 840754dcc6ca4..a7e762c352f95 100644
--- a/drivers/firmware/arm_sdei.c
+++ b/drivers/firmware/arm_sdei.c
@@ -31,7 +31,6 @@
#include <linux/slab.h>
#include <linux/smp.h>
#include <linux/spinlock.h>
-#include <linux/uaccess.h>

/*
* The call to use to reach the firmware.
@@ -1092,26 +1091,13 @@ int sdei_event_handler(struct pt_regs *regs,
struct sdei_registered_event *arg)
{
int err;
- mm_segment_t orig_addr_limit;
u32 event_num = arg->event_num;

- /*
- * Save restore 'fs'.
- * The architecture's entry code save/restores 'fs' when taking an
- * exception from the kernel. This ensures addr_limit isn't inherited
- * if you interrupted something that allowed the uaccess routines to
- * access kernel memory.
- * Do the same here because this doesn't come via the same entry code.
- */
- orig_addr_limit = force_uaccess_begin();
-
err = arg->callback(event_num, regs, arg->callback_arg);
if (err)
pr_err_ratelimited("event %u on CPU %u failed with error: %d\n",
event_num, smp_processor_id(), err);

- force_uaccess_end(orig_addr_limit);
-
return err;
}
NOKPROBE_SYMBOL(sdei_event_handler);