diff mbox series

[mickledore,12/12] gdb: fix crashes when debugging threads with Arm Pointer Authentication enabled

Message ID c46d0cfe4b18318c00390eb112edcbea8b8d6a7a.1685291299.git.steve@sakoman.com
State New
Headers show
Series [mickledore,01/12] libxfixes: Upgrade to v6.0.1 | expand

Commit Message

Steve Sakoman May 28, 2023, 5:07 p.m. UTC
From: Ross Burton <ross.burton@arm.com>

(From OE-Core rev: 8057edfcb23004b18ab8cb09b9a359346ed54db9)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
(cherry picked from commit a6120d0c7946842195f0c7624b7c3025e74e7964)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
 meta/recipes-devtools/gdb/gdb.inc             |   1 +
 ...r-valid-inferior-thread-regcache-bef.patch | 286 ++++++++++++++++++
 2 files changed, 287 insertions(+)
 create mode 100644 meta/recipes-devtools/gdb/gdb/0001-aarch64-Check-for-valid-inferior-thread-regcache-bef.patch
diff mbox series


diff --git a/meta/recipes-devtools/gdb/gdb.inc b/meta/recipes-devtools/gdb/gdb.inc
index 9457c27f8b..8589de62ff 100644
--- a/meta/recipes-devtools/gdb/gdb.inc
+++ b/meta/recipes-devtools/gdb/gdb.inc
@@ -15,6 +15,7 @@  SRC_URI = "${GNU_MIRROR}/gdb/gdb-${PV}.tar.xz \
            file://0008-Define-alignof-using-_Alignof-when-using-C11-or-newe.patch \
            file://0009-gdbserver-linux-low.cc-Fix-a-typo-in-ternary-operato.patch \
            file://add-missing-ldflags.patch \
+           file://0001-aarch64-Check-for-valid-inferior-thread-regcache-bef.patch \
 SRC_URI[sha256sum] = "115ad5c18d69a6be2ab15882d365dda2a2211c14f480b3502c6eba576e2e95a0"
diff --git a/meta/recipes-devtools/gdb/gdb/0001-aarch64-Check-for-valid-inferior-thread-regcache-bef.patch b/meta/recipes-devtools/gdb/gdb/0001-aarch64-Check-for-valid-inferior-thread-regcache-bef.patch
new file mode 100644
index 0000000000..9adf4a4db5
--- /dev/null
+++ b/meta/recipes-devtools/gdb/gdb/0001-aarch64-Check-for-valid-inferior-thread-regcache-bef.patch
@@ -0,0 +1,286 @@ 
+From b3eff3e15576229af9bae026c5c23ee694b90389 Mon Sep 17 00:00:00 2001
+From: Luis Machado <luis.machado@arm.com>
+Date: Fri, 24 Mar 2023 07:58:38 +0000
+Subject: [PATCH] aarch64: Check for valid inferior thread/regcache before
+ reading pauth registers
+Upstream-Status: Backport
+Signed-off-by: Ross Burton <ross.burton@arm.com>
+There were reports of gdb throwing internal errors when calling
+inferior_thread ()/get_current_regcache () on a system with
+Pointer Authentication enabled.
+In such cases, gdb produces the following backtrace, or a variation
+of it (for gdb's with the non-address removal implemented only in
+the aarch64-linux-tdep.c file).
+../../../repos/binutils-gdb/gdb/thread.c:86: internal-error: inferior_thread: Assertion `current_thread_ != nullptr' failed.
+A problem internal to GDB has been detected,
+further debugging may prove unreliable.
+----- Backtrace -----
+0xaaaae04a571f gdb_internal_backtrace_1
+        ../../../repos/binutils-gdb/gdb/bt-utils.c:122
+0xaaaae04a57f3 _Z22gdb_internal_backtracev
+        ../../../repos/binutils-gdb/gdb/bt-utils.c:168
+0xaaaae0b52ccf internal_vproblem
+        ../../../repos/binutils-gdb/gdb/utils.c:401
+0xaaaae0b5310b _Z15internal_verrorPKciS0_St9__va_list
+        ../../../repos/binutils-gdb/gdb/utils.c:481
+0xaaaae0e24b8f _Z18internal_error_locPKciS0_z
+        ../../../repos/binutils-gdb/gdbsupport/errors.cc:58
+0xaaaae0a88983 _Z15inferior_threadv
+        ../../../repos/binutils-gdb/gdb/thread.c:86
+0xaaaae0956c87 _Z20get_current_regcachev
+        ../../../repos/binutils-gdb/gdb/regcache.c:428
+0xaaaae035223f aarch64_remove_non_address_bits
+        ../../../repos/binutils-gdb/gdb/aarch64-tdep.c:3572
+0xaaaae03e8abb _Z31gdbarch_remove_non_address_bitsP7gdbarchm
+        ../../../repos/binutils-gdb/gdb/gdbarch.c:3109
+0xaaaae0a692d7 memory_xfer_partial
+        ../../../repos/binutils-gdb/gdb/target.c:1620
+0xaaaae0a695e3 _Z19target_xfer_partialP10target_ops13target_objectPKcPhPKhmmPm
+        ../../../repos/binutils-gdb/gdb/target.c:1684
+0xaaaae0a69e9f target_read_partial
+        ../../../repos/binutils-gdb/gdb/target.c:1937
+0xaaaae0a69fdf _Z11target_readP10target_ops13target_objectPKcPhml
+        ../../../repos/binutils-gdb/gdb/target.c:1977
+0xaaaae0a69937 _Z18target_read_memorymPhl
+        ../../../repos/binutils-gdb/gdb/target.c:1773
+0xaaaae08be523 ps_xfer_memory
+        ../../../repos/binutils-gdb/gdb/proc-service.c:90
+0xaaaae08be6db ps_pdread
+        ../../../repos/binutils-gdb/gdb/proc-service.c:124
+0x40001ed7c3b3 _td_fetch_value
+        /build/glibc-RIFKjK/glibc-2.31/nptl_db/fetch-value.c:115
+0x40001ed791ef td_ta_map_lwp2thr
+        /build/glibc-RIFKjK/glibc-2.31/nptl_db/td_ta_map_lwp2thr.c:194
+0xaaaae07f4473 thread_from_lwp
+        ../../../repos/binutils-gdb/gdb/linux-thread-db.c:413
+0xaaaae07f6d6f _ZN16thread_db_target4waitE6ptid_tP17target_waitstatus10enum_flagsI16target_wait_flagE
+        ../../../repos/binutils-gdb/gdb/linux-thread-db.c:1420
+0xaaaae0a6b33b _Z11target_wait6ptid_tP17target_waitstatus10enum_flagsI16target_wait_flagE
+        ../../../repos/binutils-gdb/gdb/target.c:2586
+0xaaaae0789cf7 do_target_wait_1
+        ../../../repos/binutils-gdb/gdb/infrun.c:3825
+0xaaaae0789e6f operator()
+        ../../../repos/binutils-gdb/gdb/infrun.c:3884
+0xaaaae078a167 do_target_wait
+        ../../../repos/binutils-gdb/gdb/infrun.c:3903
+0xaaaae078b0af _Z20fetch_inferior_eventv
+        ../../../repos/binutils-gdb/gdb/infrun.c:4314
+0xaaaae076652f _Z22inferior_event_handler19inferior_event_type
+        ../../../repos/binutils-gdb/gdb/inf-loop.c:41
+0xaaaae07dc68b handle_target_event
+        ../../../repos/binutils-gdb/gdb/linux-nat.c:4206
+0xaaaae0e25fbb handle_file_event
+        ../../../repos/binutils-gdb/gdbsupport/event-loop.cc:573
+0xaaaae0e264f3 gdb_wait_for_event
+        ../../../repos/binutils-gdb/gdbsupport/event-loop.cc:694
+0xaaaae0e24f9b _Z16gdb_do_one_eventi
+        ../../../repos/binutils-gdb/gdbsupport/event-loop.cc:217
+0xaaaae080f033 start_event_loop
+        ../../../repos/binutils-gdb/gdb/main.c:411
+0xaaaae080f1b7 captured_command_loop
+        ../../../repos/binutils-gdb/gdb/main.c:475
+0xaaaae0810b97 captured_main
+        ../../../repos/binutils-gdb/gdb/main.c:1318
+0xaaaae0810c1b _Z8gdb_mainP18captured_main_args
+        ../../../repos/binutils-gdb/gdb/main.c:1337
+0xaaaae0338453 main
+        ../../../repos/binutils-gdb/gdb/gdb.c:32
+../../../repos/binutils-gdb/gdb/thread.c:86: internal-error: inferior_thread: Assertion `current_thread_ != nullptr' failed.
+A problem internal to GDB has been detected,
+further debugging may prove unreliable.
+Quit this debugging session? (y or n)
+We also see failures across the testsuite if the tests get executed on a target
+that has native support for the pointer authentication feature. But
+gdb.base/break.exp and gdb.base/access-mem-running.exp are two examples of
+tests that run into errors and internal errors.
+This issue started after commit d88cb738e6a7a7179dfaff8af78d69250c852af1, which
+enabled more broad use of pointer authentication masks to remove non-address
+bits of pointers, but wasn't immediately detected because systems with native
+support for pointer authentication are not that common yet.
+The above crash happens because gdb is in the middle of handling an event,
+and do_target_wait_1 calls switch_to_inferior_no_thread, nullifying the
+current thread.  This means a call to inferior_thread () will assert, and
+attempting to call get_current_regcache () will also call inferior_thread (),
+resulting in an assertion as well.
+target_has_registers was one function that seemed useful for detecting these
+types of situation where we don't have a register cache. The problem with that
+is the inconsistent state of inferior_ptid, which is used by
+Despite the call to switch_to_no_thread in switch_to_inferior_no_thread from
+do_target_wait_1 in the backtrace above clearing inferior_ptid, the call to
+ps_xfer_memory sets inferior_ptid momentarily before reading memory:
+static ps_err_e
+ps_xfer_memory (const struct ps_prochandle *ph, psaddr_t addr,
+                gdb_byte *buf, size_t len, int write)
+  scoped_restore_current_inferior restore_inferior;
+  set_current_inferior (ph->thread->inf);
+  scoped_restore_current_program_space restore_current_progspace;
+  set_current_program_space (ph->thread->inf->pspace);
+  scoped_restore save_inferior_ptid = make_scoped_restore (&inferior_ptid);
+  inferior_ptid = ph->thread->ptid;
+  CORE_ADDR core_addr = ps_addr_to_core_addr (addr);
+  int ret;
+  if (write)
+    ret = target_write_memory (core_addr, buf, len);
+  else
+    ret = target_read_memory (core_addr, buf, len);
+  return (ret == 0 ? PS_OK : PS_ERR);
+Maybe this shouldn't happen, or maybe it is just an unfortunate state to be
+in. But this prevents the use of target_has_registers to guard against the
+lack of registers, since, although current_thread_ is still nullptr,
+inferior_ptid is valid and is not null_ptid.
+There is another crash scenario after we kill a previously active inferior, in
+which case the gdbarch will still say we support pointer authentication but we
+will also have no current thread (inferior_thread () will assert etc).
+If the target has support for pointer authentication, gdb needs to use
+a couple (or 4, for bare-metal) mask registers to mask off some bits of
+pointers, and for that it needs to access the registers.
+At some points, like the one from the backtrace above, there is no active
+thread/current regcache because gdb is in the middle of doing event handling
+and switching between threads.
+Simon suggested the use of inferior_ptid to fetch the register cache, as
+opposed to relying on the current register cache.  Though we need to make sure
+inferior_ptid is valid (not null_ptid), I think this works nicely.
+With inferior_ptid, we can do safety checks along the way, making sure we have
+a thread to fetch a register cache from and checking if the thread is actually
+stopped or running.
+The following patch implements this idea with safety checks to make sure we
+don't run into assertions or errors.  If any of the checks fail, we fallback to
+using a default mask to remove non-address bits of a pointer.
+I discussed with Pedro the possibility of caching the mask register values
+(which are per-process and can change mid-execution), but there isn't a good
+spot to cache those values. Besides, the mask registers can change constantly
+for bare-metal debugging when switching between exception levels.
+In some cases, it is just not possible to get access to these mask registers,
+like the case where threads are running. In those cases, using a default mask
+to remove the non-address bits should be enough.
+This can happen when we let threads run in the background and then we attempt
+to access a memory address (now that gdb is capable of reading memory even
+with threads running).  Thus gdb will attempt to remove non-address bits
+of that memory access, will attempt to access registers, running into errors.
+Regression-tested on aarch64-linux Ubuntu 20.04.
+ gdb/aarch64-linux-tdep.c | 64 ++++++++++++++++++++++++++++++----------
+ 1 file changed, 49 insertions(+), 15 deletions(-)
+diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
+index 20a041c599e..4b2915b8e99 100644
+--- a/gdb/aarch64-linux-tdep.c
++++ b/gdb/aarch64-linux-tdep.c
+@@ -57,6 +57,9 @@
+ #include "elf/common.h"
+ #include "elf/aarch64.h"
++/* For inferior_ptid and current_inferior ().  */
++#include "inferior.h"
+ /* Signal frame handling.
+       +------------+  ^
+@@ -1986,29 +1989,60 @@ aarch64_linux_decode_memtag_section (struct gdbarch *gdbarch,
+ static CORE_ADDR
+ aarch64_remove_non_address_bits (struct gdbarch *gdbarch, CORE_ADDR pointer)
+ {
+-  aarch64_gdbarch_tdep *tdep = gdbarch_tdep<aarch64_gdbarch_tdep> (gdbarch);
+   /* By default, we assume TBI and discard the top 8 bits plus the VA range
+-     select bit (55).  */
++     select bit (55).  Below we try to fetch information about pointer
++     authentication masks in order to make non-address removal more
++     precise.  */
+-  if (tdep->has_pauth ())
++  /* Check if we have an inferior first.  If not, just use the default
++     mask.
++     We use the inferior_ptid here because the pointer authentication masks
++     should be the same across threads of a process.  Since we may not have
++     access to the current thread (gdb may have switched to no inferiors
++     momentarily), we use the inferior ptid.  */
++  if (inferior_ptid != null_ptid)
+     {
+-      /* Fetch the PAC masks.  These masks are per-process, so we can just
+-	 fetch data from whatever thread we have at the moment.
++      /* If we do have an inferior, attempt to fetch its thread's thread_info
++	 struct.  */
++      thread_info *thread
++	= find_thread_ptid (current_inferior ()->process_target (),
++			    inferior_ptid);
+-	 Also, we have both a code mask and a data mask.  For now they are the
+-	 same, but this may change in the future.  */
+-      struct regcache *regs = get_current_regcache ();
+-      CORE_ADDR cmask, dmask;
++      /* If the thread is running, we will not be able to fetch the mask
++	 registers.  */
++      if (thread != nullptr && thread->state != THREAD_RUNNING)
++	{
++	  /* Otherwise, fetch the register cache and the masks.  */
++	  struct regcache *regs
++	    = get_thread_regcache (current_inferior ()->process_target (),
++				   inferior_ptid);
++	  /* Use the gdbarch from the register cache to check for pointer
++	     authentication support, as it matches the features found in
++	     that particular thread.  */
++	  aarch64_gdbarch_tdep *tdep
++	    = gdbarch_tdep<aarch64_gdbarch_tdep> (regs->arch ());
++	  /* Is there pointer authentication support?  */
++	  if (tdep->has_pauth ())
++	    {
++	      /* We have both a code mask and a data mask.  For now they are
++		 the same, but this may change in the future.  */
++	      CORE_ADDR cmask, dmask;
+-      if (regs->cooked_read (tdep->pauth_reg_base, &dmask) != REG_VALID)
+-	dmask = mask;
++	      if (regs->cooked_read (tdep->pauth_reg_base, &dmask)
++		  != REG_VALID)
++		dmask = mask;
+-      if (regs->cooked_read (tdep->pauth_reg_base + 1, &cmask) != REG_VALID)
+-	cmask = mask;
++	      if (regs->cooked_read (tdep->pauth_reg_base + 1, &cmask)
++		  != REG_VALID)
++		cmask = mask;
+-      mask |= aarch64_mask_from_pac_registers (cmask, dmask);
++	      mask |= aarch64_mask_from_pac_registers (cmask, dmask);
++	    }
++	}
+     }
+   return aarch64_remove_top_bits (pointer, mask);