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aarch64: Add GCS support for setcontext

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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>
This commit is contained in:
Szabolcs Nagy 2023-02-24 16:29:32 +00:00 • committed by Yury Khrustalev
parent 1cf59c2603
commit 9885d13b66
4 changed files with 83 additions and 9 deletions
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17
sysdeps/unix/sysv/linux/aarch64/getcontext.S
View file

@ -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]

38
sysdeps/unix/sysv/linux/aarch64/setcontext.S
View file

@ -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. */

32
sysdeps/unix/sysv/linux/aarch64/swapcontext.S
View file

@ -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:

5
sysdeps/unix/sysv/linux/aarch64/ucontext-internal.h
View file

@ -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