Kamalesh pointed out that we are getting the below call traces with
livepatched functions when we enable CONFIG_PREEMPT:
[ 495.470721] BUG: using __this_cpu_read() in preemptible [00000000] code: cat/8394
[ 495.471167] caller is is_current_kprobe_addr+0x30/0x90
[ 495.471171] CPU: 4 PID: 8394 Comm: cat Tainted: G K 4.13.0-rc7-nnr+ #95
[ 495.471173] Call Trace:
[ 495.471178] [c00000008fd9b960] [c0000000009f039c] dump_stack+0xec/0x160 (unreliable)
[ 495.471184] [c00000008fd9b9a0] [c00000000059169c] check_preemption_disabled+0x15c/0x170
[ 495.471187] [c00000008fd9ba30] [c000000000046460] is_current_kprobe_addr+0x30/0x90
[ 495.471191] [c00000008fd9ba60] [c00000000004e9a0] ftrace_call+0x1c/0xb8
[ 495.471195] [c00000008fd9bc30] [c000000000376fd8] seq_read+0x238/0x5c0
[ 495.471199] [c00000008fd9bcd0] [c0000000003cfd78] proc_reg_read+0x88/0xd0
[ 495.471203] [c00000008fd9bd00] [c00000000033e5d4] __vfs_read+0x44/0x1b0
[ 495.471206] [c00000008fd9bd90] [c0000000003402ec] vfs_read+0xbc/0x1b0
[ 495.471210] [c00000008fd9bde0] [c000000000342138] SyS_read+0x68/0x110
[ 495.471214] [c00000008fd9be30] [c00000000000bc6c] system_call+0x58/0x6c
Commit c05b8c4474 ("powerpc/kprobes: Skip livepatch_handler() for
jprobes") introduced a helper is_current_kprobe_addr() to help determine
if the current function has been livepatched or if it has a jprobe
installed, both of which modify the NIP. This was subsequently renamed
to __is_active_jprobe().
In the case of a jprobe, kprobe_ftrace_handler() disables pre-emption
before calling into setjmp_pre_handler() which returns without disabling
pre-emption. This is done to ensure that the jprobe handler won't
disappear beneath us if the jprobe is unregistered between the
setjmp_pre_handler() and the subsequent longjmp_break_handler() called
from the jprobe handler. Due to this, we can use __this_cpu_read() in
__is_active_jprobe() with the pre-emption check as we know that
pre-emption will be disabled.
However, if this function has been livepatched, we are still doing this
check and when we do so, pre-emption won't necessarily be disabled. This
results in the call trace shown above.
Fix this by only invoking __is_active_jprobe() when pre-emption is
disabled. And since we now guard this within a pre-emption check, we can
instead use raw_cpu_read() to get the current_kprobe value skipping the
check done by __this_cpu_read().
Fixes: c05b8c4474 ("powerpc/kprobes: Skip livepatch_handler() for jprobes")
Reported-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
In commit c05b8c4474 ("powerpc/kprobes: Skip livepatch_handler() for
jprobes"), we added a helper is_current_kprobe_addr() to help detect if
the modified regs->nip was due to a jprobe or livepatch. Masami felt
that the function name was not quite clear. To that end, this patch
renames is_current_kprobe_addr() to __is_active_jprobe() and adds a
comment to (hopefully) better clarify the purpose of this helper. The
helper has also now been moved to kprobes-ftrace.c so that it is only
available for KPROBES_ON_FTRACE.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Allow kprobes to be placed on ftrace _mcount() call sites. This optimization
avoids the use of a trap, by riding on ftrace infrastructure.
This depends on HAVE_DYNAMIC_FTRACE_WITH_REGS which depends on MPROFILE_KERNEL,
which is only currently enabled on powerpc64le with newer toolchains.
Based on the x86 code by Masami.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
