linux-stable.git/arch/arm64/kernel/entry-common.c, branch linux-5.15.y

arm64: split EL0/EL1 UNDEF handlers

2023-10-19T21:05:38+00:00

commit 61d64a376ea80f9097e7ea599bcd68671b836dc6 upstream.

In general, exceptions taken from EL1 need to be handled separately from
exceptions taken from EL0, as the logic to handle the two cases can be
significantly divergent, and exceptions taken from EL1 typically have
more stringent requirements on locking and instrumentation.

Subsequent patches will rework the way EL1 UNDEFs are handled in order
to address longstanding soundness issues with instrumentation and RCU.
In preparation for that rework, this patch splits the existing
do_undefinstr() handler into separate do_el0_undef() and do_el1_undef()
handlers.

Prior to this patch, do_undefinstr() was marked with NOKPROBE_SYMBOL(),
preventing instrumentation via kprobes. However, do_undefinstr() invokes
other code which can be instrumented, and:

* For UNDEFINED exceptions taken from EL0, there is no risk of recursion
  within kprobes. Therefore it is safe for do_el0_undef to be
  instrumented with kprobes, and it does not need to be marked with
  NOKPROBE_SYMBOL().

* For UNDEFINED exceptions taken from EL1, either:

  (a) The exception is has been taken when manipulating SSBS; these cases
      are limited and do not occur within code that can be invoked
      recursively via kprobes. Hence, in these cases instrumentation
      with kprobes is benign.

  (b) The exception has been taken for an unknown reason, as other than
      manipulating SSBS we do not expect to take UNDEFINED exceptions
      from EL1. Any handling of these exception is best-effort.

  ... and in either case, marking do_el1_undef() with NOKPROBE_SYMBOL()
  isn't sufficient to prevent recursion via kprobes as functions it
  calls (including die()) are instrumentable via kprobes.

  Hence, it's not worthwhile to mark do_el1_undef() with
  NOKPROBE_SYMBOL(). The same applies to do_el1_bti() and do_el1_fpac(),
  so their NOKPROBE_SYMBOL() annotations are also removed.

Aside from the new instrumentability, there should be no functional
change as a result of this patch.

Signed-off-by: Mark Rutland 
Cc: Catalin Marinas 
Cc: James Morse 
Cc: Joey Gouly 
Cc: Peter Zijlstra 
Cc: Will Deacon 
Link: https://lore.kernel.org/r/20221019144123.612388-3-mark.rutland@arm.com
Signed-off-by: Will Deacon 
Signed-off-by: Jinjie Ruan 
Signed-off-by: Greg Kroah-Hartman

arm64: allow kprobes on EL0 handlers

2023-10-19T21:05:38+00:00

commit b3a0c010e900a9f89dcd99f10bd8f7538d21b0a9 upstream.

Currently do_sysinstr() and do_cp15instr() are marked with
NOKPROBE_SYMBOL(). However, these are only called for exceptions taken
from EL0, and there is no risk of recursion in kprobes, so this is not
necessary.

Remove the NOKPROBE_SYMBOL() annotation, and rename the two functions to
more clearly indicate that these are solely for exceptions taken from
EL0, better matching the names used by the lower level entry points in
entry-common.c.

Signed-off-by: Mark Rutland 
Cc: Catalin Marinas 
Cc: James Morse 
Cc: Joey Gouly 
Cc: Peter Zijlstra 
Cc: Will Deacon 
Link: https://lore.kernel.org/r/20221019144123.612388-2-mark.rutland@arm.com
Signed-off-by: Will Deacon 
Signed-off-by: Jinjie Ruan 
Signed-off-by: Greg Kroah-Hartman

arm64: rework BTI exception handling

2023-10-19T21:05:38+00:00

commit 830a2a4d853f2c4a1e4606aa03341b7f273b0e9b upstream.

If a BTI exception is taken from EL1, the entry code will treat this as
an unhandled exception and will panic() the kernel. This is inconsistent
with the way we handle FPAC exceptions, which have a dedicated handler
and only necessarily kill the thread from which the exception was taken
from, and we don't log all the information that could be relevant to
debug the issue.

The code in do_bti() has:

	BUG_ON(!user_mode(regs));

... and it seems like the intent was to call this for EL1 BTI
exceptions, as with FPAC, but this was omitted due to an oversight.

This patch adds separate EL0 and EL1 BTI exception handlers, with the
latter calling die() directly to report the original context the BTI
exception was taken from. This matches our handling of FPAC exceptions.

Prior to this patch, a BTI failure is reported as:

| Unhandled 64-bit el1h sync exception on CPU0, ESR 0x0000000034000002 -- BTI
| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.19.0-rc3-00131-g7d937ff0221d-dirty #9
| Hardware name: linux,dummy-virt (DT)
| pstate: 20400809 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=-c)
| pc : test_bti_callee+0x4/0x10
| lr : test_bti_caller+0x1c/0x28
| sp : ffff80000800bdf0
| x29: ffff80000800bdf0 x28: 0000000000000000 x27: 0000000000000000
| x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
| x23: ffff80000a2b8000 x22: 0000000000000000 x21: 0000000000000000
| x20: ffff8000099fa5b0 x19: ffff800009ff7000 x18: fffffbfffda37000
| x17: 3120676e696d7573 x16: 7361202c6e6f6974 x15: 0000000041a90000
| x14: 0040000000000041 x13: 0040000000000001 x12: ffff000001a90000
| x11: fffffbfffda37480 x10: 0068000000000703 x9 : 0001000040000000
| x8 : 0000000000090000 x7 : 0068000000000f03 x6 : 0060000000000f83
| x5 : ffff80000a2b6000 x4 : ffff0000028d0000 x3 : ffff800009f78378
| x2 : 0000000000000000 x1 : 0000000040210000 x0 : ffff8000080257e4
| Kernel panic - not syncing: Unhandled exception
| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.19.0-rc3-00131-g7d937ff0221d-dirty #9
| Hardware name: linux,dummy-virt (DT)
| Call trace:
|  dump_backtrace.part.0+0xcc/0xe0
|  show_stack+0x18/0x5c
|  dump_stack_lvl+0x64/0x80
|  dump_stack+0x18/0x34
|  panic+0x170/0x360
|  arm64_exit_nmi.isra.0+0x0/0x80
|  el1h_64_sync_handler+0x64/0xd0
|  el1h_64_sync+0x64/0x68
|  test_bti_callee+0x4/0x10
|  smp_cpus_done+0xb0/0xbc
|  smp_init+0x7c/0x8c
|  kernel_init_freeable+0x128/0x28c
|  kernel_init+0x28/0x13c
|  ret_from_fork+0x10/0x20

With this patch applied, a BTI failure is reported as:

| Internal error: Oops - BTI: 0000000034000002 [#1] PREEMPT SMP
| Modules linked in:
| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.19.0-rc3-00132-g0ad98265d582-dirty #8
| Hardware name: linux,dummy-virt (DT)
| pstate: 20400809 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=-c)
| pc : test_bti_callee+0x4/0x10
| lr : test_bti_caller+0x1c/0x28
| sp : ffff80000800bdf0
| x29: ffff80000800bdf0 x28: 0000000000000000 x27: 0000000000000000
| x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
| x23: ffff80000a2b8000 x22: 0000000000000000 x21: 0000000000000000
| x20: ffff8000099fa5b0 x19: ffff800009ff7000 x18: fffffbfffda37000
| x17: 3120676e696d7573 x16: 7361202c6e6f6974 x15: 0000000041a90000
| x14: 0040000000000041 x13: 0040000000000001 x12: ffff000001a90000
| x11: fffffbfffda37480 x10: 0068000000000703 x9 : 0001000040000000
| x8 : 0000000000090000 x7 : 0068000000000f03 x6 : 0060000000000f83
| x5 : ffff80000a2b6000 x4 : ffff0000028d0000 x3 : ffff800009f78378
| x2 : 0000000000000000 x1 : 0000000040210000 x0 : ffff800008025804
| Call trace:
|  test_bti_callee+0x4/0x10
|  smp_cpus_done+0xb0/0xbc
|  smp_init+0x7c/0x8c
|  kernel_init_freeable+0x128/0x28c
|  kernel_init+0x28/0x13c
|  ret_from_fork+0x10/0x20
| Code: d50323bf d53cd040 d65f03c0 d503233f (d50323bf)

Signed-off-by: Mark Rutland 
Reviewed-by: Mark Brown 
Reviewed-by: Anshuman Khandual 
Cc: Alexandru Elisei 
Cc: Amit Daniel Kachhap 
Cc: James Morse 
Cc: Will Deacon 
Link: https://lore.kernel.org/r/20220913101732.3925290-6-mark.rutland@arm.com
Signed-off-by: Catalin Marinas 
Signed-off-by: Jinjie Ruan 
Signed-off-by: Greg Kroah-Hartman

arm64: rework FPAC exception handling

2023-10-19T21:05:38+00:00

commit a1fafa3b24a70461bbf3e5c0770893feb0a49292 upstream.

If an FPAC exception is taken from EL1, the entry code will call
do_ptrauth_fault(), where due to:

	BUG_ON(!user_mode(regs))

... the kernel will report a problem within do_ptrauth_fault() rather
than reporting the original context the FPAC exception was taken from.
The pt_regs and ESR value reported will be from within
do_ptrauth_fault() and the code dump will be for the BRK in BUG_ON(),
which isn't sufficient to debug the cause of the original exception.

This patch makes the reporting better by having separate EL0 and EL1
FPAC exception handlers, with the latter calling die() directly to
report the original context the FPAC exception was taken from.

Note that we only need to prevent kprobes of the EL1 FPAC handler, since
the EL0 FPAC handler cannot be called recursively.

For consistency with do_el0_svc*(), I've named the split functions
do_el{0,1}_fpac() rather than do_el{0,1}_ptrauth_fault(). I've also
clarified the comment to not imply there are casues other than FPAC
exceptions.

Prior to this patch FPAC exceptions are reported as:

| kernel BUG at arch/arm64/kernel/traps.c:517!
| Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
| Modules linked in:
| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.19.0-rc3-00130-g9c8a180a1cdf-dirty #12
| Hardware name: FVP Base RevC (DT)
| pstate: 00400009 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : do_ptrauth_fault+0x3c/0x40
| lr : el1_fpac+0x34/0x54
| sp : ffff80000a3bbc80
| x29: ffff80000a3bbc80 x28: ffff0008001d8000 x27: 0000000000000000
| x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
| x23: 0000000020400009 x22: ffff800008f70fa4 x21: ffff80000a3bbe00
| x20: 0000000072000000 x19: ffff80000a3bbcb0 x18: fffffbfffda37000
| x17: 3120676e696d7573 x16: 7361202c6e6f6974 x15: 0000000081a90000
| x14: 0040000000000041 x13: 0040000000000001 x12: ffff000001a90000
| x11: fffffbfffda37480 x10: 0068000000000703 x9 : 0001000080000000
| x8 : 0000000000090000 x7 : 0068000000000f03 x6 : 0060000000000783
| x5 : ffff80000a3bbcb0 x4 : ffff0008001d8000 x3 : 0000000072000000
| x2 : 0000000000000000 x1 : 0000000020400009 x0 : ffff80000a3bbcb0
| Call trace:
|  do_ptrauth_fault+0x3c/0x40
|  el1h_64_sync_handler+0xc4/0xd0
|  el1h_64_sync+0x64/0x68
|  test_pac+0x8/0x10
|  smp_init+0x7c/0x8c
|  kernel_init_freeable+0x128/0x28c
|  kernel_init+0x28/0x13c
|  ret_from_fork+0x10/0x20
| Code: 97fffe5e a8c17bfd d50323bf d65f03c0 (d4210000)

With this patch applied FPAC exceptions are reported as:

| Internal error: Oops - FPAC: 0000000072000000 [#1] PREEMPT SMP
| Modules linked in:
| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.19.0-rc3-00132-g78846e1c4757-dirty #11
| Hardware name: FVP Base RevC (DT)
| pstate: 20400009 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : test_pac+0x8/0x10
| lr : 0x0
| sp : ffff80000a3bbe00
| x29: ffff80000a3bbe00 x28: 0000000000000000 x27: 0000000000000000
| x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
| x23: ffff80000a2c8000 x22: 0000000000000000 x21: 0000000000000000
| x20: ffff8000099fa5b0 x19: ffff80000a007000 x18: fffffbfffda37000
| x17: 3120676e696d7573 x16: 7361202c6e6f6974 x15: 0000000081a90000
| x14: 0040000000000041 x13: 0040000000000001 x12: ffff000001a90000
| x11: fffffbfffda37480 x10: 0068000000000703 x9 : 0001000080000000
| x8 : 0000000000090000 x7 : 0068000000000f03 x6 : 0060000000000783
| x5 : ffff80000a2c6000 x4 : ffff0008001d8000 x3 : ffff800009f88378
| x2 : 0000000000000000 x1 : 0000000080210000 x0 : ffff000001a90000
| Call trace:
|  test_pac+0x8/0x10
|  smp_init+0x7c/0x8c
|  kernel_init_freeable+0x128/0x28c
|  kernel_init+0x28/0x13c
|  ret_from_fork+0x10/0x20
| Code: d50323bf d65f03c0 d503233f aa1f03fe (d50323bf)

Signed-off-by: Mark Rutland 
Reviewed-by: Mark Brown 
Reviewed-by: Anshuman Khandual 
Cc: Alexandru Elisei 
Cc: Amit Daniel Kachhap 
Cc: James Morse 
Cc: Will Deacon 
Link: https://lore.kernel.org/r/20220913101732.3925290-5-mark.rutland@arm.com
Signed-off-by: Catalin Marinas 
Signed-off-by: Jinjie Ruan 
Signed-off-by: Greg Kroah-Hartman

arm64: consistently pass ESR_ELx to die()

2023-10-19T21:05:38+00:00

commit 0f2cb928a1547ae8f89e80a4b8df2c6c02ae5f96 upstream.

Currently, bug_handler() and kasan_handler() call die() with '0' as the
'err' value, whereas die_kernel_fault() passes the ESR_ELx value.

For consistency, this patch ensures we always pass the ESR_ELx value to
die(). As this is only called for exceptions taken from kernel mode,
there should be no user-visible change as a result of this patch.

For UNDEFINED exceptions, I've had to modify do_undefinstr() and its
callers to pass the ESR_ELx value. In all cases the ESR_ELx value had
already been read and was available.

Signed-off-by: Mark Rutland 
Cc: Mark Brown 
Cc: Alexandru Elisei 
Cc: Amit Daniel Kachhap 
Cc: James Morse 
Cc: Will Deacon 
Reviewed-by: Anshuman Khandual 
Reviewed-by: Mark Brown 
Link: https://lore.kernel.org/r/20220913101732.3925290-4-mark.rutland@arm.com
Signed-off-by: Catalin Marinas 
Signed-off-by: Jinjie Ruan 
Signed-off-by: Greg Kroah-Hartman

arm64: Treat ESR_ELx as a 64-bit register

2022-12-31T12:13:58+00:00

[ Upstream commit 8d56e5c5a99ce1d17d39ce5a8260e42c2a2d7682 ]

In the initial release of the ARM Architecture Reference Manual for
ARMv8-A, the ESR_ELx registers were defined as 32-bit registers. This
changed in 2018 with version D.a (ARM DDI 0487D.a) of the architecture,
when they became 64-bit registers, with bits [63:32] defined as RES0. In
version G.a, a new field was added to ESR_ELx, ISS2, which covers bits
[36:32].  This field is used when the Armv8.7 extension FEAT_LS64 is
implemented.

As a result of the evolution of the register width, Linux stores it as
both a 64-bit value and a 32-bit value, which hasn't affected correctness
so far as Linux only uses the lower 32 bits of the register.

Make the register type consistent and always treat it as 64-bit wide. The
register is redefined as an "unsigned long", which is an unsigned
double-word (64-bit quantity) for the LP64 machine (aapcs64 [1], Table 1,
page 14). The type was chosen because "unsigned int" is the most frequent
type for ESR_ELx and because FAR_ELx, which is used together with ESR_ELx
in exception handling, is also declared as "unsigned long". The 64-bit type
also makes adding support for architectural features that use fields above
bit 31 easier in the future.

The KVM hypervisor will receive a similar update in a subsequent patch.

[1] https://github.com/ARM-software/abi-aa/releases/download/2021Q3/aapcs64.pdf

Signed-off-by: Alexandru Elisei 
Reviewed-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20220425114444.368693-4-alexandru.elisei@arm.com
Signed-off-by: Catalin Marinas 
Stable-dep-of: 0bb1fbffc631 ("arm64: mm: kfence: only handle translation faults")
Signed-off-by: Sasha Levin

arm64: entry: avoid kprobe recursion

2022-11-10T17:15:39+00:00

commit 024f4b2e1f874934943eb2d3d288ebc52c79f55c upstream.

The cortex_a76_erratum_1463225_debug_handler() function is called when
handling debug exceptions (and synchronous exceptions from BRK
instructions), and so is called when a probed function executes. If the
compiler does not inline cortex_a76_erratum_1463225_debug_handler(), it
can be probed.

If cortex_a76_erratum_1463225_debug_handler() is probed, any debug
exception or software breakpoint exception will result in recursive
exceptions leading to a stack overflow. This can be triggered with the
ftrace multiple_probes selftest, and as per the example splat below.

This is a regression caused by commit:

  6459b8469753e9fe ("arm64: entry: consolidate Cortex-A76 erratum 1463225 workaround")

... which removed the NOKPROBE_SYMBOL() annotation associated with the
function.

My intent was that cortex_a76_erratum_1463225_debug_handler() would be
inlined into its caller, el1_dbg(), which is marked noinstr and cannot
be probed. Mark cortex_a76_erratum_1463225_debug_handler() as
__always_inline to ensure this.

Example splat prior to this patch (with recursive entries elided):

| # echo p cortex_a76_erratum_1463225_debug_handler > /sys/kernel/debug/tracing/kprobe_events
| # echo p do_el0_svc >> /sys/kernel/debug/tracing/kprobe_events
| # echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
| Insufficient stack space to handle exception!
| ESR: 0x0000000096000047 -- DABT (current EL)
| FAR: 0xffff800009cefff0
| Task stack:     [0xffff800009cf0000..0xffff800009cf4000]
| IRQ stack:      [0xffff800008000000..0xffff800008004000]
| Overflow stack: [0xffff00007fbc00f0..0xffff00007fbc10f0]
| CPU: 0 PID: 145 Comm: sh Not tainted 6.0.0 #2
| Hardware name: linux,dummy-virt (DT)
| pstate: 604003c5 (nZCv DAIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : arm64_enter_el1_dbg+0x4/0x20
| lr : el1_dbg+0x24/0x5c
| sp : ffff800009cf0000
| x29: ffff800009cf0000 x28: ffff000002c74740 x27: 0000000000000000
| x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
| x23: 00000000604003c5 x22: ffff80000801745c x21: 0000aaaac95ac068
| x20: 00000000f2000004 x19: ffff800009cf0040 x18: 0000000000000000
| x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
| x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
| x11: 0000000000000010 x10: ffff800008c87190 x9 : ffff800008ca00d0
| x8 : 000000000000003c x7 : 0000000000000000 x6 : 0000000000000000
| x5 : 0000000000000000 x4 : 0000000000000000 x3 : 00000000000043a4
| x2 : 00000000f2000004 x1 : 00000000f2000004 x0 : ffff800009cf0040
| Kernel panic - not syncing: kernel stack overflow
| CPU: 0 PID: 145 Comm: sh Not tainted 6.0.0 #2
| Hardware name: linux,dummy-virt (DT)
| Call trace:
|  dump_backtrace+0xe4/0x104
|  show_stack+0x18/0x4c
|  dump_stack_lvl+0x64/0x7c
|  dump_stack+0x18/0x38
|  panic+0x14c/0x338
|  test_taint+0x0/0x2c
|  panic_bad_stack+0x104/0x118
|  handle_bad_stack+0x34/0x48
|  __bad_stack+0x78/0x7c
|  arm64_enter_el1_dbg+0x4/0x20
|  el1h_64_sync_handler+0x40/0x98
|  el1h_64_sync+0x64/0x68
|  cortex_a76_erratum_1463225_debug_handler+0x0/0x34
...
|  el1h_64_sync_handler+0x40/0x98
|  el1h_64_sync+0x64/0x68
|  cortex_a76_erratum_1463225_debug_handler+0x0/0x34
...
|  el1h_64_sync_handler+0x40/0x98
|  el1h_64_sync+0x64/0x68
|  cortex_a76_erratum_1463225_debug_handler+0x0/0x34
|  el1h_64_sync_handler+0x40/0x98
|  el1h_64_sync+0x64/0x68
|  do_el0_svc+0x0/0x28
|  el0t_64_sync_handler+0x84/0xf0
|  el0t_64_sync+0x18c/0x190
| Kernel Offset: disabled
| CPU features: 0x0080,00005021,19001080
| Memory Limit: none
| ---[ end Kernel panic - not syncing: kernel stack overflow ]---

With this patch, cortex_a76_erratum_1463225_debug_handler() is inlined
into el1_dbg(), and el1_dbg() cannot be probed:

| # echo p cortex_a76_erratum_1463225_debug_handler > /sys/kernel/debug/tracing/kprobe_events
| sh: write error: No such file or directory
| # grep -w cortex_a76_erratum_1463225_debug_handler /proc/kallsyms | wc -l
| 0
| # echo p el1_dbg > /sys/kernel/debug/tracing/kprobe_events
| sh: write error: Invalid argument
| # grep -w el1_dbg /proc/kallsyms | wc -l
| 1

Fixes: 6459b8469753 ("arm64: entry: consolidate Cortex-A76 erratum 1463225 workaround")
Cc:  # 5.12.x
Signed-off-by: Mark Rutland 
Cc: Will Deacon 
Link: https://lore.kernel.org/r/20221017090157.2881408-1-mark.rutland@arm.com
Signed-off-by: Catalin Marinas 
Signed-off-by: Greg Kroah-Hartman

lockdep: Fix -Wunused-parameter for _THIS_IP_

2022-09-20T10:39:42+00:00

[ Upstream commit 8b023accc8df70e72f7704d29fead7ca914d6837 ]

While looking into a bug related to the compiler's handling of addresses
of labels, I noticed some uses of _THIS_IP_ seemed unused in lockdep.
Drive by cleanup.

-Wunused-parameter:
kernel/locking/lockdep.c:1383:22: warning: unused parameter 'ip'
kernel/locking/lockdep.c:4246:48: warning: unused parameter 'ip'
kernel/locking/lockdep.c:4844:19: warning: unused parameter 'ip'

Signed-off-by: Nick Desaulniers 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Waiman Long 
Link: https://lore.kernel.org/r/20220314221909.2027027-1-ndesaulniers@google.com
Stable-dep-of: 54c3931957f6 ("tracing: hold caller_addr to hardirq_{enable,disable}_ip")
Signed-off-by: Sasha Levin

arm64: entry: call exit_to_user_mode() from C

2021-08-05T13:10:32+00:00

When handling an exception from EL0, we perform the entry work in that
exception's C handler, and once the C handler has finished, we return
back to the entry assembly. Subsequently in the common `ret_to_user`
assembly we perform the exit work that balances with the entry work.
This can be somewhat difficult to follow, and makes it hard to rework
the return paths (e.g. to pass additional context to the exit code, or
to have exception return logic for specific exceptions).

This patch reworks the entry code such that each EL0 C exception handler
is responsible for both the entry and exit work. This clearly balances
the two (and will permit additional variation in future), and avoids an
unnecessary bounce between assembly and C in the common case, leaving
`ret_from_fork` as the only place assembly has to call the exit code.
This means that the exit work is now inlined into the C handler, which
is already the case for the entry work, and allows the compiler to
generate better code (e.g. by immediately returning when there is no
exit work to perform).

To align with other exception entry/exit helpers, enter_from_user_mode()
is updated to take the EL0 pt_regs as a parameter, though this is
currently unused.

There should be no functional change as a result of this patch. However,
this should lead to slightly better backtraces when an error is
encountered within do_notify_resume(), as the C handler should appear in
the backtrace, indicating the specific exception that the kernel was
entered with.

Signed-off-by: Mark Rutland 
Cc: James Morse 
Cc: Joey Gouly 
Cc: Marc Zyngier 
Cc: Will Deacon 
Reviewed-by: Joey Gouly 
Link: https://lore.kernel.org/r/20210802140733.52716-5-mark.rutland@arm.com
Signed-off-by: Catalin Marinas

arm64: entry: move bulk of ret_to_user to C

2021-08-05T13:09:49+00:00

In `ret_to_user` we perform some conditional work depending on the
thread flags, then perform some IRQ/context tracking which is intended
to balance with the IRQ/context tracking performed in the entry C code.

For simplicity and consistency, it would be preferable to move this all
to C. As a step towards that, this patch moves the conditional work and
IRQ/context tracking into a C helper function. To aid bisectability,
this is called from the `ret_to_user` assembly, and a subsequent patch
will move the call to C code.

As local_daif_mask() handles all necessary tracing and PMR manipulation,
we no longer need to handle this explicitly. As we call
exit_to_user_mode() directly, the `user_enter_irqoff` macro is no longer
used, and can be removed. As enter_from_user_mode() and
exit_to_user_mode() are no longer called from assembly, these can be
made static, and as these are typically very small, they are marked
__always_inline to avoid the overhead of a function call.

For now, enablement of single-step is left in entry.S, and for this we
still need to read the flags in ret_to_user(). It is safe to read this
separately as TIF_SINGLESTEP is not part of _TIF_WORK_MASK.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland 
Cc: James Morse 
Cc: Joey Gouly 
Cc: Marc Zyngier 
Cc: Will Deacon 
Reviewed-by: Joey Gouly 
Link: https://lore.kernel.org/r/20210802140733.52716-4-mark.rutland@arm.com
[catalin.marinas@arm.com: removed unused gic_prio_kentry_setup macro]
Signed-off-by: Catalin Marinas