[PATCH v5 06/23] aarch64: Add GCS support for setcontext
Wilco Dijkstra
Wilco.Dijkstra@arm.com
Wed Dec 11 14:23:23 GMT 2024
Hi Yury,
OK.
Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cheers,
Wilco
From: Szabolcs Nagy <szabolcs.nagy@arm.com>
Userspace ucontext needs to store GCSPR, it does not have to be
compatible with the kernel ucontext. For now we use the linux
struct gcs_context layout but only use the gcspr field from it.
Similar implementation to the longjmp code, supports switching GCS
if the target GCS is capped, and unwinding a continuous GCS to a
previous state.
---
sysdeps/unix/sysv/linux/aarch64/getcontext.S | 17 ++++++++-
sysdeps/unix/sysv/linux/aarch64/setcontext.S | 38 +++++++++++++++++++
sysdeps/unix/sysv/linux/aarch64/swapcontext.S | 32 ++++++++++++----
.../sysv/linux/aarch64/ucontext-internal.h | 5 +++
4 files changed, 83 insertions(+), 9 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/aarch64/getcontext.S b/sysdeps/unix/sysv/linux/aarch64/getcontext.S
index e5b69c9a82..a8ea9d9a9b 100644
--- a/sysdeps/unix/sysv/linux/aarch64/getcontext.S
+++ b/sysdeps/unix/sysv/linux/aarch64/getcontext.S
@@ -83,9 +83,24 @@ ENTRY(__getcontext)
mrs x4, fpcr
str w4, [x3, oFPCR - oFPSR]
- /* Write the termination context extension header. */
add x2, x2, #FPSIMD_CONTEXT_SIZE
+ /* Save the GCSPR. */
+ mov x16, 1 /* _CHKFEAT_GCS */
+ CHKFEAT_X16
+ tbnz x16, 0, L(gcs_done)
+ mov w3, #(GCS_MAGIC & 0xffff)
+ movk w3, #(GCS_MAGIC >> 16), lsl #16
+ str w3, [x2, #oHEAD + oMAGIC]
+ mov w3, #GCS_CONTEXT_SIZE
+ str w3, [x2, #oHEAD + oSIZE]
+ MRS_GCSPR (x4)
+ add x4, x4, 8 /* GCS state right after getcontext returns. */
+ str x4, [x2, #oGCSPR]
+ add x2, x2, #GCS_CONTEXT_SIZE
+L(gcs_done):
+
+ /* Write the termination context extension header. */
str wzr, [x2, #oHEAD + oMAGIC]
str wzr, [x2, #oHEAD + oSIZE]
diff --git a/sysdeps/unix/sysv/linux/aarch64/setcontext.S b/sysdeps/unix/sysv/linux/aarch64/setcontext.S
index ba659438c5..e52d7d926a 100644
--- a/sysdeps/unix/sysv/linux/aarch64/setcontext.S
+++ b/sysdeps/unix/sysv/linux/aarch64/setcontext.S
@@ -130,6 +130,44 @@ ENTRY (__setcontext)
ldr w4, [x3, oFPCR - oFPSR]
msr fpcr, x4
+ /* Restore the GCS. */
+ mov x16, 1 /* _CHKFEAT_GCS */
+ CHKFEAT_X16
+ tbnz x16, 0, L(gcs_done)
+ /* Get target GCS from GCS context. */
+ ldr w1, [x2, #oHEAD + oSIZE]
+ add x2, x2, x1
+ mov w3, #(GCS_MAGIC & 0xffff)
+ movk w3, #(GCS_MAGIC >> 16), lsl #16
+ ldr w1, [x2, #oHEAD + oMAGIC]
+ cmp w1, w3
+ b.ne L(gcs_done)
+ ldr x3, [x2, #oGCSPR]
+ MRS_GCSPR (x2)
+ mov x4, x3
+ /* x2: GCSPR now. x3, x4: target GCSPR. x5, x6: tmp regs. */
+L(gcs_scan):
+ cmp x2, x4
+ b.eq L(gcs_pop)
+ sub x4, x4, 8
+ /* Check for a cap token. */
+ ldr x5, [x4]
+ and x6, x4, 0xfffffffffffff000
+ orr x6, x6, 1
+ cmp x5, x6
+ b.ne L(gcs_scan)
+L(gcs_switch):
+ add x2, x4, 8
+ GCSSS1 (x4)
+ GCSSS2 (xzr)
+L(gcs_pop):
+ cmp x2, x3
+ b.eq L(gcs_done)
+ GCSPOPM (xzr)
+ add x2, x2, 8
+ b L(gcs_pop)
+L(gcs_done):
+
2:
ldr x16, [x0, oPC]
/* Restore arg registers. */
diff --git a/sysdeps/unix/sysv/linux/aarch64/swapcontext.S b/sysdeps/unix/sysv/linux/aarch64/swapcontext.S
index f049140d35..ffc7d724f5 100644
--- a/sysdeps/unix/sysv/linux/aarch64/swapcontext.S
+++ b/sysdeps/unix/sysv/linux/aarch64/swapcontext.S
@@ -32,8 +32,15 @@ ENTRY(__swapcontext)
And set up x1 to become the return address of the caller, so we
can return there with a normal RET instead of an indirect jump. */
stp xzr, x30, [x0, oX0 + 0 * SZREG]
+
+ /* With GCS, swapcontext calls are followed by BTI J, otherwise
+ we have to be compatible with old BTI enabled binaries. */
+ mov x16, 1 /* _CHKFEAT_GCS */
+ CHKFEAT_X16
+ tbz x16, 0, L(skip_x30_redirect)
/* Arrange the oucp context to return to 2f. */
adr x30, 2f
+L(skip_x30_redirect):
stp x18, x19, [x0, oX0 + 18 * SZREG]
stp x20, x21, [x0, oX0 + 20 * SZREG]
@@ -72,14 +79,27 @@ ENTRY(__swapcontext)
mrs x4, fpcr
str w4, [x3, #oFPCR - oFPSR]
- /* Write the termination context extension header. */
add x2, x2, #FPSIMD_CONTEXT_SIZE
+ /* Save the GCSPR. */
+ tbnz x16, 0, L(gcs_done)
+ mov w3, #(GCS_MAGIC & 0xffff)
+ movk w3, #(GCS_MAGIC >> 16), lsl #16
+ str w3, [x2, #oHEAD + oMAGIC]
+ mov w3, #GCS_CONTEXT_SIZE
+ str w3, [x2, #oHEAD + oSIZE]
+ MRS_GCSPR (x4)
+ add x4, x4, 8 /* GCSPR of the caller. */
+ str x4, [x2, #oGCSPR]
+ add x2, x2, #GCS_CONTEXT_SIZE
+L(gcs_done):
+
+ /* Write the termination context extension header. */
str wzr, [x2, #oHEAD + oMAGIC]
str wzr, [x2, #oHEAD + oSIZE]
/* Preserve ucp. */
- mov x21, x1
+ mov x9, x1
/* rt_sigprocmask (SIG_SETMASK, &ucp->uc_sigmask, &oucp->uc_sigmask,
_NSIG8) */
@@ -93,12 +113,8 @@ ENTRY(__swapcontext)
svc 0
cbnz x0, 1f
- mov x22, x30
- mov x0, x21
- bl JUMPTARGET (__setcontext)
- mov x30, x22
- RET
-
+ mov x0, x9
+ b JUMPTARGET (__setcontext)
1:
b C_SYMBOL_NAME(__syscall_error)
2:
diff --git a/sysdeps/unix/sysv/linux/aarch64/ucontext-internal.h b/sysdeps/unix/sysv/linux/aarch64/ucontext-internal.h
index 096d5fb7c7..84f5365c0e 100644
--- a/sysdeps/unix/sysv/linux/aarch64/ucontext-internal.h
+++ b/sysdeps/unix/sysv/linux/aarch64/ucontext-internal.h
@@ -43,3 +43,8 @@
#define oX21 (oX0 + 21*8)
#define oFP (oX0 + 29*8)
#define oLR (oX0 + 30*8)
+
+/* Use kernel layout for saving GCSPR in ucontext. */
+#define GCS_MAGIC 0x47435300
+#define GCS_CONTEXT_SIZE 32
+#define oGCSPR 8
--
2.39.5
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