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35b6b28e69
When branch target identifiers are in use, code reachable via an
indirect branch requires a BTI landing pad at the branch target site.
When building FTRACE_WITH_REGS atop patchable-function-entry, we miss
BTIs at the start start of the `ftrace_caller` and `ftrace_regs_caller`
trampolines, and when these are called from a module via a PLT (which
will use a `BR X16`), we will encounter a BTI failure, e.g.
| # insmod lkdtm.ko
| lkdtm: No crash points registered, enable through debugfs
| # echo function_graph > /sys/kernel/debug/tracing/current_tracer
| # cat /sys/kernel/debug/provoke-crash/DIRECT
| Unhandled 64-bit el1h sync exception on CPU0, ESR 0x34000001 -- BTI
| CPU: 0 PID: 174 Comm: cat Not tainted 5.16.0-rc2-dirty #3
| Hardware name: linux,dummy-virt (DT)
| pstate: 60400405 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=jc)
| pc : ftrace_caller+0x0/0x3c
| lr : lkdtm_debugfs_open+0xc/0x20 [lkdtm]
| sp : ffff800012e43b00
| x29: ffff800012e43b00 x28: 0000000000000000 x27: ffff800012e43c88
| x26: 0000000000000000 x25: 0000000000000000 x24: ffff0000c171f200
| x23: ffff0000c27b1e00 x22: ffff0000c2265240 x21: ffff0000c23c8c30
| x20: ffff8000090ba380 x19: 0000000000000000 x18: 0000000000000000
| x17: 0000000000000000 x16: ffff80001002bb4c x15: 0000000000000000
| x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000900ff0
| x11: ffff0000c4166310 x10: ffff800012e43b00 x9 : ffff8000104f2384
| x8 : 0000000000000001 x7 : 0000000000000000 x6 : 000000000000003f
| x5 : 0000000000000040 x4 : ffff800012e43af0 x3 : 0000000000000001
| x2 : ffff8000090b0000 x1 : ffff0000c171f200 x0 : ffff0000c23c8c30
| Kernel panic - not syncing: Unhandled exception
| CPU: 0 PID: 174 Comm: cat Not tainted 5.16.0-rc2-dirty #3
| Hardware name: linux,dummy-virt (DT)
| Call trace:
| dump_backtrace+0x0/0x1a4
| show_stack+0x24/0x30
| dump_stack_lvl+0x68/0x84
| dump_stack+0x1c/0x38
| panic+0x168/0x360
| arm64_exit_nmi.isra.0+0x0/0x80
| el1h_64_sync_handler+0x68/0xd4
| el1h_64_sync+0x78/0x7c
| ftrace_caller+0x0/0x3c
| do_dentry_open+0x134/0x3b0
| vfs_open+0x38/0x44
| path_openat+0x89c/0xe40
| do_filp_open+0x8c/0x13c
| do_sys_openat2+0xbc/0x174
| __arm64_sys_openat+0x6c/0xbc
| invoke_syscall+0x50/0x120
| el0_svc_common.constprop.0+0xdc/0x100
| do_el0_svc+0x84/0xa0
| el0_svc+0x28/0x80
| el0t_64_sync_handler+0xa8/0x130
| el0t_64_sync+0x1a0/0x1a4
| SMP: stopping secondary CPUs
| Kernel Offset: disabled
| CPU features: 0x0,00000f42,da660c5f
| Memory Limit: none
| ---[ end Kernel panic - not syncing: Unhandled exception ]---
Fix this by adding the required `BTI C`, as we only require these to be
reachable via BL for direct calls or BR X16/X17 for PLTs. For now, these
are open-coded in the function prologue, matching the style of the
`__hwasan_tag_mismatch` trampoline.
In future we may wish to consider adding a new SYM_CODE_START_*()
variant which has an implicit BTI.
When ftrace is built atop mcount, the trampolines are marked with
SYM_FUNC_START(), and so get an implicit BTI. We may need to change
these over to SYM_CODE_START() in future for RELIABLE_STACKTRACE, in
case we need to apply special care aroud the return address being
rewritten.
Fixes:
|
||
|---|---|---|
| .. | ||
| probes | ||
| vdso | ||
| vdso32 | ||
| .gitignore | ||
| acpi.c | ||
| acpi_numa.c | ||
| acpi_parking_protocol.c | ||
| alternative.c | ||
| armv8_deprecated.c | ||
| asm-offsets.c | ||
| cacheinfo.c | ||
| cpu-reset.S | ||
| cpu_errata.c | ||
| cpu_ops.c | ||
| cpufeature.c | ||
| cpuidle.c | ||
| cpuinfo.c | ||
| crash_core.c | ||
| crash_dump.c | ||
| debug-monitors.c | ||
| efi-entry.S | ||
| efi-header.S | ||
| efi-rt-wrapper.S | ||
| efi.c | ||
| entry-common.c | ||
| entry-fpsimd.S | ||
| entry-ftrace.S | ||
| entry.S | ||
| fpsimd.c | ||
| ftrace.c | ||
| head.S | ||
| hibernate-asm.S | ||
| hibernate.c | ||
| hw_breakpoint.c | ||
| hyp-stub.S | ||
| idle.c | ||
| idreg-override.c | ||
| image-vars.h | ||
| image.h | ||
| io.c | ||
| irq.c | ||
| jump_label.c | ||
| kaslr.c | ||
| kexec_image.c | ||
| kgdb.c | ||
| kuser32.S | ||
| machine_kexec.c | ||
| machine_kexec_file.c | ||
| Makefile | ||
| module-plts.c | ||
| module.c | ||
| mte.c | ||
| paravirt.c | ||
| patching.c | ||
| pci.c | ||
| perf_callchain.c | ||
| perf_event.c | ||
| perf_regs.c | ||
| pointer_auth.c | ||
| process.c | ||
| proton-pack.c | ||
| psci.c | ||
| ptrace.c | ||
| reloc_test_core.c | ||
| reloc_test_syms.S | ||
| relocate_kernel.S | ||
| return_address.c | ||
| sdei.c | ||
| setup.c | ||
| signal.c | ||
| signal32.c | ||
| sigreturn32.S | ||
| sleep.S | ||
| smccc-call.S | ||
| smp.c | ||
| smp_spin_table.c | ||
| stacktrace.c | ||
| suspend.c | ||
| sys.c | ||
| sys32.c | ||
| sys_compat.c | ||
| syscall.c | ||
| time.c | ||
| topology.c | ||
| trace-events-emulation.h | ||
| traps.c | ||
| vdso-wrap.S | ||
| vdso.c | ||
| vdso32-wrap.S | ||
| vmlinux.lds.S | ||