Re: [Tarantool-patches] [PATCH luajit 3/3][v3] Add stack check to pcall/xpcall.

[Sergey Bronnikov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

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Hi, Sergey,

thanks for review! See my comments below.

Sergey

On 3/12/26 13:16, Sergey Kaplun via Tarantool-patches wrote:
> Hi, Sergey!
> Thanks for the patch!
> Please, fix my comments below.
>
> Don't forget to add the corresponding iterative changes.
>
> On 12.03.26, Sergey Bronnikov wrote:
>> From: Mike Pall <mike>
>>
>> Analyzed by Peter Cawley.
>>
>> (cherry picked from commit a4c1640432a9d8a60624cdc8065b15078c228e36)
>>
>> The patch adds the stack check to fast functions `pcall()` and
>> `xpcall()`.
> Please add more verbose description:
>
> | (cherry picked from commit a4c1640432a9d8a60624cdc8065b15078c228e36)
> |
> | The `pcall()` and `xpcall()` calls in GC64 mode require 2 slots. This
> | means that all arguments should be moved up during emitting of the frame
> | link to the stack. Hence, this may cause stack overflow without the
> | corresponding check.
> |
> | This patch adds the corresponding checks to the VM. Non-GC64 VMs are
> | updated as well for the consistency.
Updated
>> Sergey Bronnikov:
>> * added the description and the test for the problem
>>
>> Part of tarantool/tarantool#12134
>> ---
>>   src/vm_arm.dasc                               |  7 ++++
>>   src/vm_arm64.dasc                             |  8 +++++
>>   src/vm_mips.dasc                              | 10 +++++-
>>   src/vm_mips64.dasc                            | 14 ++++++--
>>   src/vm_ppc.dasc                               |  9 +++++
>>   src/vm_x64.dasc                               |  6 ++++
>>   src/vm_x86.dasc                               |  6 ++++
>>   ...048-fix-stack-checks-vararg-calls.test.lua | 35 ++++++++++++++++++-
>>   8 files changed, 90 insertions(+), 5 deletions(-)
>>
>> diff --git a/src/vm_arm.dasc b/src/vm_arm.dasc
>> index 7095e660..efe9dcb2 100644
>> --- a/src/vm_arm.dasc
>> +++ b/src/vm_arm.dasc
> <snipped>
>
>> diff --git a/src/vm_arm64.dasc b/src/vm_arm64.dasc
>> index 5ef37243..074c1f31 100644
>> --- a/src/vm_arm64.dasc
>> +++ b/src/vm_arm64.dasc
> <snipped>
>
>> diff --git a/src/vm_mips.dasc b/src/vm_mips.dasc
>> index 32caabf7..69d09d52 100644
>> --- a/src/vm_mips.dasc
>> +++ b/src/vm_mips.dasc
> <snipped>
>
>> diff --git a/src/vm_mips64.dasc b/src/vm_mips64.dasc
>> index 6c2975b4..4e60ee07 100644
>> --- a/src/vm_mips64.dasc
>> +++ b/src/vm_mips64.dasc
>> @@ -1418,8 +1418,12 @@ static void build_subroutines(BuildCtx *ctx)
>>     |//-- Base library: catch errors ----------------------------------------
>>     |
>>     |.ffunc pcall
>> +  |  ld TMP1, L->maxstack
>> +  |  daddu TMP2, BASE,NARGS8:RC
>> +  |  sltu AT, TMP1, TMP2
>> +  |  bnez AT, ->fff_fallback
>> +  |.  lbu TMP3, DISPATCH_GL(hookmask)(DISPATCH)
>>     |  daddiuNARGS8:RC,NARGS8:RC, -8
>> -  |  lbu TMP3, DISPATCH_GL(hookmask)(DISPATCH)
>>     |  bltzNARGS8:RC, ->fff_fallback
>>     |.   move TMP2, BASE
>>     |   daddiu BASE, BASE, 16
>> @@ -1440,8 +1444,12 @@ static void build_subroutines(BuildCtx *ctx)
>>     |.  nop
>>     |
>>     |.ffunc xpcall
>> -  |  daddiuNARGS8:TMP0,NARGS8:RC, -16
> This neglets the first patch in the series. See the comment below.
>
>> -  |  ld CARG1, 0(BASE)
>> +  |  ld TMP1, L->maxstack
>> +  |  daddu TMP2, BASE,NARGS8:RC
>> +  |  sltu AT, TMP1, TMP2
>> +  |  bnez AT, ->fff_fallback
>> +  |.  ld CARG1, 0(BASE)
>> +  |  daddiuNARGS8:RC,NARGS8:RC, -16
> This line is incorrect. This neglets the 1st patch in the series.
>
> It should be
> | |  daddiuNARGS8:TMP0,NARGS8:RC, -16

Right. However, probably we should leave this line near ".ffunc xpcall". 
What do you think?

Now updated as the following:

--- a/src/vm_mips64.dasc
+++ b/src/vm_mips64.dasc
@@ -1449,7 +1449,7 @@ static void build_subroutines(BuildCtx *ctx)
    |  sltu AT, TMP1, TMP2
    |  bnez AT, ->fff_fallback
    |.  ld CARG1, 0(BASE)
-  |  daddiu NARGS8:RC, NARGS8:RC, -16
+  |  daddiu NARGS8:TMP0, NARGS8:RC, -16
    |   ld CARG2, 8(BASE)
    |    bltz NARGS8:TMP0, ->fff_fallback
    |.    lbu TMP1, DISPATCH_GL(hookmask)(DISPATCH)

>
>>     |   ld CARG2, 8(BASE)
>>     |    bltzNARGS8:TMP0, ->fff_fallback
>>     |.    lbu TMP1, DISPATCH_GL(hookmask)(DISPATCH)
>> diff --git a/src/vm_ppc.dasc b/src/vm_ppc.dasc
>> index 980ad897..f2ea933b 100644
>> --- a/src/vm_ppc.dasc
>> +++ b/src/vm_ppc.dasc
> <snipped>
>
>> diff --git a/src/vm_x64.dasc b/src/vm_x64.dasc
>> index 8b6781a6..c57b76b7 100644
>> --- a/src/vm_x64.dasc
>> +++ b/src/vm_x64.dasc
> <snipped>
>
>> diff --git a/src/vm_x86.dasc b/src/vm_x86.dasc
>> index 7c11c78e..36804d11 100644
>> --- a/src/vm_x86.dasc
>> +++ b/src/vm_x86.dasc
> <snipped>
>
>> diff --git a/test/tarantool-tests/lj-1048-fix-stack-checks-vararg-calls.test.lua b/test/tarantool-tests/lj-1048-fix-stack-checks-vararg-calls.test.lua
>> index 3a8ad63d..ad8b151b 100644
>> --- a/test/tarantool-tests/lj-1048-fix-stack-checks-vararg-calls.test.lua
>> +++ b/test/tarantool-tests/lj-1048-fix-stack-checks-vararg-calls.test.lua
>> @@ -5,7 +5,7 @@ local tap = require('tap')
>>   -- See alsohttps://github.com/LuaJIT/LuaJIT/issues/1048.
>>   local test = tap.test('lj-1048-fix-stack-checks-vararg-calls')
>>   
>> -test:plan(2)
>> +test:plan(5)
>>   
>>   -- The test case demonstrates a segmentation fault due to stack
>>   -- overflow by recursive calling `pcall()`. The functions are
>> @@ -50,4 +50,37 @@ pcall(coroutine.wrap(looper), prober_2, 0)
>>   
>>   test:ok(true, 'no stack overflow with metamethod')
>>   
>> +-- The testcases demonstrates a stack overflow in
>> +-- `pcall()`/xpcall()` triggered using metamethod `__call`.
>> +
>> +t = coroutine.wrap(setmetatable)({}, { __call = pcall })
> I've meant the following:
>
> | t = setmetatable({}, { __call = pcall })
> | coroutine.wrap(function() t() end)()
>
Updated

@@ -53,7 +53,8 @@ test:ok(true, 'no stack overflow with metamethod')
  -- The testcases demonstrates a stack overflow in
  -- `pcall()`/xpcall()` triggered using metamethod `__call`.

-t = coroutine.wrap(setmetatable)({}, { __call = pcall })
+t = setmetatable({}, { __call = pcall })
+coroutine.wrap(function() t() end)()

test:ok(true, 'no stack overflow with metamethod __call with pcall()')


>> +
>> +test:ok(true, 'no stack overflow with metamethod __call with pcall()')
>> +
>> +t = coroutine.wrap(setmetatable)({}, { __call = xpcall })
> I've meant the following:
>
> | t = setmetatable({}, { __call = xpcall })
> | coroutine.wrap(function() t() end)()
>
> But this won't work since the second amount of xpcall must be the
> function. So, this test case is invalid. We must to duplicate the second
> approach with `xpcall()`
>
> This works fine.
> | LUA_PATH="src/?.lua;;" gdb --args src/luajit -e '
> | local t = {}
> | local function xpcall_wrapper()
> |   return xpcall(unpack(t))
> | end
> |
> | local N_ITERATIONS = 200
> |
> | for i = 1, N_ITERATIONS do
> |   t[i], t[i + 1], t[i + 2] = xpcall, type, {}
> |   coroutine.wrap(xpcall_wrapper)()
> | end
> | '

Updated:

diff --git 
a/test/tarantool-tests/lj-1048-fix-stack-checks-vararg-calls.test.lua 
b/test/tarantool-tests/lj-1048-fix-stack-checks-vararg-calls.test.lua
index 6395dfaa..825568f9 100644
--- a/test/tarantool-tests/lj-1048-fix-stack-checks-vararg-calls.test.lua
+++ b/test/tarantool-tests/lj-1048-fix-stack-checks-vararg-calls.test.lua
@@ -58,7 +58,17 @@ coroutine.wrap(function() t() end)()

test:ok(true, 'no stack overflow with metamethod __call with pcall()')

-t = coroutine.wrap(setmetatable)({}, { __call = xpcall })
+t = {}
+local function xpcall_wrapper()
+  return xpcall(unpack(t))
+end
+
+local N_ITERATIONS_1 = 200
+
+for i = 1, N_ITERATIONS_1 do
+  t[i], t[i + 1], t[i + 2] = xpcall, type, {}
+  coroutine.wrap(xpcall_wrapper)()
+end

test:ok(true, 'no stack overflow with metamethod __call with xpcall()')

@@ -67,19 +77,19 @@ test:ok(true, 'no stack overflow with metamethod 
__call with xpcall()')
  -- triggered using `unpack()`.

  t = {}
-local function f()
+local function pcall_wrapper()
    return pcall(unpack(t))
  end

--- The problem is only reproduced on LuaJIT GC64 and is best
+-- The problem is only reproduced on LuaJIT GC64 and is better
  -- reproduced under Valgrind than AddressSanitizer. The chosen
  -- value was found experimentally and always results in an attempt
  -- to write beyond the allocated memory.
-local N_ITERATIONS = 200
+local N_ITERATIONS_2 = 200

-for i = 1, N_ITERATIONS do
+for i = 1, N_ITERATIONS_2 do
    t[i], t[i + 1], t[i + 2] = pcall, type, {}
-  coroutine.wrap(f)()
+  coroutine.wrap(pcall_wrapper)()
  end

test:ok(true, 'no stack overflow with unpacked pcalls')

>> +
>> +test:ok(true, 'no stack overflow with metamethod __call with xpcall()')
>> +
>> +-- The testcase demonstrates a stack overflow in
>> +-- `pcall()`/`xpcall()` similar to the first testcase, but it is
>> +-- triggered using `unpack()`.
>> +
>> +t = {}
>> +local function f()
> Lets name it `pcall_wrapper()`
>
@@ -66,7 +68,7 @@ test:ok(true, 'no stack overflow with metamethod 
__call with xpcall()')
  -- triggered using `unpack()`.

  t = {}
-local function f()
+local function pcall_wrapper()
    return pcall(unpack(t))
  end

@@ -78,7 +80,7 @@ local N_ITERATIONS = 200

  for i = 1, N_ITERATIONS do
    t[i], t[i + 1], t[i + 2] = pcall, type, {}
-  coroutine.wrap(f)()
+  coroutine.wrap(pcall_wrapper)()
  end

test:ok(true, 'no stack overflow with unpacked pcalls')

>> +  return pcall(unpack(t))
>> +end
>> +
>> +-- The problem is only reproduced on LuaJIT GC64 and is best
> Typo: s/best/better/
    return pcall(unpack(t))
  end

--- The problem is only reproduced on LuaJIT GC64 and is best
+-- The problem is only reproduced on LuaJIT GC64 and is better
  -- reproduced under Valgrind than AddressSanitizer. The chosen
  -- value was found experimentally and always results in an attempt
  -- to write beyond the allocated memory.

>
>> +-- reproduced under Valgrind than AddressSanitizer. The chosen
>> +-- value was found experimentally and always results in an attempt
>> +-- to write beyond the allocated memory.
>> +local N_ITERATIONS = 200
>> +
>> +for i = 1, N_ITERATIONS do
>> +  t[i], t[i + 1], t[i + 2] = pcall, type, {}
>> +  coroutine.wrap(f)()
>> +end
>> +
>> +test:ok(true, 'no stack overflow with unpacked pcalls')
>> +
>>   test:done(true)
>> -- 
>> 2.43.0
>>

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