aarch64: Add GCS support for setcontext

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.

Reviewed-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

diff --git a/sysdeps/unix/sysv/linux/aarch64/getcontext.S b/sysdeps/unix/sysv/linux/aarch64/getcontext.S
index 8b18d859a05bc8846d998a63b3fae127d59ceb13..d9dd066051e707a307054a125f64b5725339eaa2 100644 (file)
--- 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 633442ecf6326e02abf82e3ae2c8ac5b07d51ed9..848229ff2676894cdbd87b2c620161a41a90ff54 100644 (file)
--- 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 2a68d385219c66e95e70accac8ff6cb5cbab6a96..893a9028664179fac2e56b12865d28dcdc54eb98 100644 (file)
--- 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 d8e88c2f9f7d563a5522304e065f9c84532a8327..841984223144684da33171f0b54eb26eebf9f2fd 100644 (file)
--- 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