+ proc-fix-pie-proc-empty-vm-proc-pid-vm-tests.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: proc: fix PIE proc-empty-vm, proc-pid-vm tests
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     proc-fix-pie-proc-empty-vm-proc-pid-vm-tests.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/proc-fix-pie-proc-empty-vm-proc-pid-vm-tests.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Alexey Dobriyan <adobriyan@gmail.com>
Subject: proc: fix PIE proc-empty-vm, proc-pid-vm tests
Date: Fri, 6 Jan 2023 22:30:14 +0300

vsyscall detection code uses direct call to the beginning of
the vsyscall page:

	asm ("call %P0" :: "i" (0xffffffffff600000))

It generates "call rel32" instruction but it is not relocated if binary
is PIE, so binary segfaults into random userspace address and vsyscall
page status is detected incorrectly.

Do more direct:

	asm ("call *%rax")

which doesn't do need any relocaltions.

Mark g_vsyscall as volatile for a good measure, I didn't find instruction
setting it to 0. Now the code is obviously correct:

	xor	eax, eax
	mov	rdi, rbp
	mov	rsi, rbp
	mov	DWORD PTR [rip+0x2d15], eax      # g_vsyscall = 0
	mov	rax, 0xffffffffff600000
	call	rax
	mov	DWORD PTR [rip+0x2d02], 1        # g_vsyscall = 1
	mov	eax, DWORD PTR ds:0xffffffffff600000
	mov	DWORD PTR [rip+0x2cf1], 2        # g_vsyscall = 2
	mov	edi, [rip+0x2ceb]                # exit(g_vsyscall)
	call	exit

Note: fixed proc-empty-vm test oopses 5.19.0-28-generic kernel
	but this is separate story.

Link: https://lkml.kernel.org/r/Y7h2xvzKLg36DSq8@p183
Fixes: 5bc73bb3451b9 ("proc: test how it holds up with mapping'less process")
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reported-by: Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>
Tested-by: Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/proc/proc-empty-vm.c |   12 +++++++-----
 tools/testing/selftests/proc/proc-pid-vm.c   |    9 +++++----
 2 files changed, 12 insertions(+), 9 deletions(-)

--- a/tools/testing/selftests/proc/proc-empty-vm.c~proc-fix-pie-proc-empty-vm-proc-pid-vm-tests
+++ a/tools/testing/selftests/proc/proc-empty-vm.c
@@ -25,6 +25,7 @@
 #undef NDEBUG
 #include <assert.h>
 #include <errno.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -41,7 +42,7 @@
  * 1: vsyscall VMA is --xp		vsyscall=xonly
  * 2: vsyscall VMA is r-xp		vsyscall=emulate
  */
-static int g_vsyscall;
+static volatile int g_vsyscall;
 static const char *g_proc_pid_maps_vsyscall;
 static const char *g_proc_pid_smaps_vsyscall;
 
@@ -147,11 +148,12 @@ static void vsyscall(void)
 
 		g_vsyscall = 0;
 		/* gettimeofday(NULL, NULL); */
+		uint64_t rax = 0xffffffffff600000;
 		asm volatile (
-			"call %P0"
-			:
-			: "i" (0xffffffffff600000), "D" (NULL), "S" (NULL)
-			: "rax", "rcx", "r11"
+			"call *%[rax]"
+			: [rax] "+a" (rax)
+			: "D" (NULL), "S" (NULL)
+			: "rcx", "r11"
 		);
 
 		g_vsyscall = 1;
--- a/tools/testing/selftests/proc/proc-pid-vm.c~proc-fix-pie-proc-empty-vm-proc-pid-vm-tests
+++ a/tools/testing/selftests/proc/proc-pid-vm.c
@@ -257,11 +257,12 @@ static void vsyscall(void)
 
 		g_vsyscall = 0;
 		/* gettimeofday(NULL, NULL); */
+		uint64_t rax = 0xffffffffff600000;
 		asm volatile (
-			"call %P0"
-			:
-			: "i" (0xffffffffff600000), "D" (NULL), "S" (NULL)
-			: "rax", "rcx", "r11"
+			"call *%[rax]"
+			: [rax] "+a" (rax)
+			: "D" (NULL), "S" (NULL)
+			: "rcx", "r11"
 		);
 
 		g_vsyscall = 1;
_

Patches currently in -mm which might be from adobriyan@gmail.com are

proc-fix-pie-proc-empty-vm-proc-pid-vm-tests.patch
proc-mark-proc-cmdline-as-permanent.patch