Re: [PATCH] powerpc/vdso: Fix multiple issues with sys_call_table
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2020-03-19 01:10:07
Also in:
lkml
Anton Blanchard [off-list ref] writes:
The VDSO exports a bitmap of valid syscalls. vdso_setup_syscall_map()
sets this up, but there are both little and big endian bugs. The issue
is with:
if (sys_call_table[i] != sys_ni_syscall)
On little endian, instead of comparing pointers to the two functions,
we compare the first two instructions of each function. If a function
happens to have the same first two instructions as sys_ni_syscall, then
we have a spurious match and mark the instruction as not implemented.
Fix this by removing the inline declarations.
On big endian we have a further issue where sys_ni_syscall is a function
descriptor and sys_call_table[] holds pointers to the instruction text.
Fix this by using dereference_kernel_function_descriptor().
Cc: stable@vger.kernel.org
Signed-off-by: Anton Blanchard <redacted>That's some pretty epic breakage. Is it even worth keeping, or should we just rip it out and declare that the syscall map is junk? Userspace can hardly rely on it given it's been this broken for so long. If not it would be really nice to have a selftest of this stuff so we can verify it works and not break it again in future. cheers
quoted hunk ↗ jump to hunk
---diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c index b9a108411c0d..d186b729026e 100644 --- a/arch/powerpc/kernel/vdso.c +++ b/arch/powerpc/kernel/vdso.c@@ -17,6 +17,7 @@ #include <linux/elf.h> #include <linux/security.h> #include <linux/memblock.h> +#include <linux/syscalls.h> #include <asm/pgtable.h> #include <asm/processor.h>@@ -30,6 +31,7 @@ #include <asm/vdso.h> #include <asm/vdso_datapage.h> #include <asm/setup.h> +#include <asm/syscall.h> #undef DEBUG@@ -644,19 +646,16 @@ static __init int vdso_setup(void) static void __init vdso_setup_syscall_map(void) { unsigned int i; - extern unsigned long *sys_call_table; -#ifdef CONFIG_PPC64 - extern unsigned long *compat_sys_call_table; -#endif - extern unsigned long sys_ni_syscall; + unsigned long ni_syscall; + ni_syscall = (unsigned long)dereference_kernel_function_descriptor(sys_ni_syscall); for (i = 0; i < NR_syscalls; i++) { #ifdef CONFIG_PPC64 - if (sys_call_table[i] != sys_ni_syscall) + if (sys_call_table[i] != ni_syscall) vdso_data->syscall_map_64[i >> 5] |= 0x80000000UL >> (i & 0x1f); - if (compat_sys_call_table[i] != sys_ni_syscall) + if (compat_sys_call_table[i] != ni_syscall) vdso_data->syscall_map_32[i >> 5] |= 0x80000000UL >> (i & 0x1f); #else /* CONFIG_PPC64 */