[PATCH v2] ntdll: Avoid overwriting parameters with context in call_user_apc_dispatcher() on x86.

[Paul Gofman]

Fixes crash in 32 bit kernel32 file test. The crash is not always reproducible
as the issue depends on stack layout.

Signed-off-by: Paul Gofman 
---
v2:
    - remove leftover debug changes.

dlls/ntdll/unix/signal_i386.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/dlls/ntdll/unix/signal_i386.c b/dlls/ntdll/unix/signal_i386.c
index 4d8eeb2072c..58b79940773 100644
--- a/dlls/ntdll/unix/signal_i386.c
+++ b/dlls/ntdll/unix/signal_i386.c
@@ -1688,15 +1688,18 @@ __ASM_GLOBAL_FUNC( call_user_apc_dispatcher,
                    "movl %esp,%ebx\n\t"
                    "cmpl %esp,%esi\n\t"
                    "cmovbl %esi,%esp\n\t"
+                   "pushl 20(%ebx)\n\t"          /* func */
+                   "pushl 16(%ebx)\n\t"          /* arg2 */
+                   "pushl 12(%ebx)\n\t"          /* arg1 */
+                   "movl 8(%ebx),%ebx\n\t"       /* ctx */
                    "movl $0x00010007,(%esi)\n\t" /* context.ContextFlags = CONTEXT_FULL */
                    "pushl %esi\n\t"              /* context */
                    "pushl $0xfffffffe\n\t"
                    "call " __ASM_STDCALL("NtGetContextThread",8) "\n\t"
                    "movl $0xc0,0xb0(%esi)\n"     /* context.Eax = STATUS_USER_APC */
-                   "movl 20(%ebx),%eax\n\t"      /* func */
-                   "movl 16(%ebx),%ecx\n\t"      /* arg2 */
-                   "movl 12(%ebx),%edx\n\t"      /* arg1 */
-                   "movl 8(%ebx),%ebx\n\t"       /* ctx */
+                   "popl %edx\n\t"
+                   "popl %ecx\n\t"
+                   "popl %eax\n\t"
                    "leal -20(%esi),%esp\n\t"
                    "movl %eax,16(%esp)\n"        /* func */
                    "2:\tmovl %ecx,12(%esp)\n\t"  /* arg2 */

[Michael Stefaniuc]

This fixes the 32 bit kernel32 file test for me too. I don't see a crash but one
CPU being pegged at 100%.

bye
    michael

On 11/12/20 3:20 PM, Paul Gofman wrote:
> Fixes crash in 32 bit kernel32 file test. The crash is not always reproducible
> as the issue depends on stack layout.
> Signed-off-by: Paul Gofman
>
> v2:
>     - remove leftover debug changes.
>
> dlls/ntdll/unix/signal_i386.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/dlls/ntdll/unix/signal_i386.c b/dlls/ntdll/unix/signal_i386.c
> index 4d8eeb2072c..58b79940773 100644
> --- a/dlls/ntdll/unix/signal_i386.c
> +++ b/dlls/ntdll/unix/signal_i386.c
> @@ -1688,15 +1688,18 @@ __ASM_GLOBAL_FUNC( call_user_apc_dispatcher,
>                     "movl %esp,%ebx\n\t"
>                     "cmpl %esp,%esi\n\t"
>                     "cmovbl %esi,%esp\n\t"
> -
>               "pushl 20(%ebx)\n\t"          /* func */
> -
>               "pushl 16(%ebx)\n\t"          /* arg2 */
> -
>               "pushl 12(%ebx)\n\t"          /* arg1 */
> -
>               "movl 8(%ebx),%ebx\n\t"       /* ctx */
>               "movl $0x00010007,(%esi)\n\t" /* context.ContextFlags = CONTEXT_FULL */
>               "pushl %esi\n\t"              /* context */
>               "pushl $0xfffffffe\n\t"
>               "call " __ASM_STDCALL("NtGetContextThread",8) "\n\t"
>               "movl $0xc0,0xb0(%esi)\n"     /* context.Eax = STATUS_USER_APC */
> -
>               "movl 20(%ebx),%eax\n\t"      /* func */
> -
>               "movl 16(%ebx),%ecx\n\t"      /* arg2 */
> -
>               "movl 12(%ebx),%edx\n\t"      /* arg1 */
> -
>               "movl 8(%ebx),%ebx\n\t"       /* ctx */
> -
>               "popl %edx\n\t"
> -
>               "popl %ecx\n\t"
> -
>               "popl %eax\n\t"
>               "leal -20(%esi),%esp\n\t"
>               "movl %eax,16(%esp)\n"        /* func */
>               "2:\tmovl %ecx,12(%esp)\n\t"  /* arg2 */