diff options
Diffstat (limited to 'gitlab/issues_text/target_arm/host_missing/accel_TCG/998')
| -rw-r--r-- | gitlab/issues_text/target_arm/host_missing/accel_TCG/998 | 60 |
1 files changed, 0 insertions, 60 deletions
diff --git a/gitlab/issues_text/target_arm/host_missing/accel_TCG/998 b/gitlab/issues_text/target_arm/host_missing/accel_TCG/998 deleted file mode 100644 index be2ff866b..000000000 --- a/gitlab/issues_text/target_arm/host_missing/accel_TCG/998 +++ /dev/null @@ -1,60 +0,0 @@ -AArch64: SCTLR_EL1.BT0 set incorrectly in user mode -Description of problem: -PACIASP normally acts as a BTI landing pad, but not in every situation. When SCTLR_EL1.BT is set, PACIASP checks that the indirect branch originates from X16 or X17 when the indirect branch is taken from a BTI guarded area. Linux sets this bit, ideally QEMU-user should too. This sample program should crash with a SIGILL if QEMU is working correctly, otherwise it will crash with a SIGSEGV. - - #include <stdint.h> - #include <stdlib.h> - #include <unistd.h> - #include <string.h> - #include <stdio.h> - #include <sys/mman.h> - - // PACIASP is a valid BTI landing pad, but there are some conditions - // under Linux which sets SCTLR_ELx.BT0 = 1. In this mode, a branch - // onto a PACIASP landing pad is only valid if it originates from - // x16 or x17 (i.e. br x17 is OK, br x3 is not). - // More info on page D5-4851 of the Arm Architecture Reference Manual (ARM DDI 0487H.a). - - // Sample function which starts with a paciasp instruction - // (comes from -mbranch-protection=pac-ret+leaf) - void indirect_fn(int i) { - // paciasp instruction inserted here - should crash with SIGILL here if everything's operating OK. - i = i+1; - // Can't access this function from the copied location, so will segfault. - fprintf(stderr, "reachable\n"); - } - - int main(int argc, char **argv) { - // It's difficult to get a whole binary BTI compatible without the appropriate crtbegin etc - // so instead map a page and copy the sample function there. - void *e = mmap(0, getpagesize(), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); - if (e == MAP_FAILED) { - return 1; - } - memcpy(e, (void*)indirect_fn, 64); - mprotect(e, getpagesize(), PROT_READ | PROT_EXEC | PROT_BTI); - - // paciasp is a valid landing pad if the branch comes from an unprotected area, - // so to ensure that we're protected - assemble an intermediate shim that's also PROT_BTI. - void *f = mmap(0, getpagesize(), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); - if (f == MAP_FAILED) { - return 1; - } - uint32_t *x = (uint32_t*)f; - x[0] = 0xd503245fuL; // bti c - x[1] = 0xd61f0060uL; // br x1 - n.b. must be BR - mprotect(f, getpagesize(), PROT_READ | PROT_EXEC | PROT_BTI); - - // Jump to the shim - asm volatile ( - "mov x3, %0\n" - "mov x2, %1\n" - "blr x2\n" - : : "p"(e), "p"(f) : "x2", "x3"); - - // Execution should not reach here - return 1; - } -Steps to reproduce: -1. Compile with `clang-12 -g --sysroot=/work/home/fedora-rootfs/fedora_aarch64 -o sample --target=aarch64-linux-gnu -mbranch-protection=pac-ret+leaf -march=armv8-a -O1 -g sample.c` or similar. -2. Run with `../qemu/build/qemu-aarch64 --cpu max -L ~/fedora-rootfs/fedora_aarch64 sample` |