6.12-stable review patch. If anyone has any objections, please let me know.
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From: Omar Sandoval osandov@fb.com
commit 5973a62efa34c80c9a4e5eac1fca6f6209b902af upstream.
Since the referenced fixes commit, the kernel's .text section is only mapped starting from _stext; the region [_text, _stext) is omitted. As a result, other vmalloc/vmap allocations may use the virtual addresses nominally in the range [_text, _stext). This address reuse confuses multiple things:
1. crash_prepare_elf64_headers() sets up a segment in /proc/vmcore mapping the entire range [_text, _end) to [__pa_symbol(_text), __pa_symbol(_end)). Reading an address in [_text, _stext) from /proc/vmcore therefore gives the incorrect result. 2. Tools doing symbolization (either by reading /proc/kallsyms or based on the vmlinux ELF file) will incorrectly identify vmalloc/vmap allocations in [_text, _stext) as kernel symbols.
In practice, both of these issues affect the drgn debugger. Specifically, there were cases where the vmap IRQ stacks for some CPUs were allocated in [_text, _stext). As a result, drgn could not get the stack trace for a crash in an IRQ handler because the core dump contained invalid data for the IRQ stack address. The stack addresses were also symbolized as being in the _text symbol.
Fix this by bringing back the mapping of [_text, _stext), but now make it non-executable and read-only. This prevents other allocations from using it while still achieving the original goal of not mapping unpredictable data as executable. Other than the changed protection, this is effectively a revert of the fixes commit.
Fixes: e2a073dde921 ("arm64: omit [_text, _stext) from permanent kernel mapping") Cc: stable@vger.kernel.org Signed-off-by: Omar Sandoval osandov@fb.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kernel/pi/map_kernel.c | 6 ++++++ arch/arm64/kernel/setup.c | 4 ++-- arch/arm64/mm/init.c | 2 +- arch/arm64/mm/mmu.c | 14 +++++++++----- 4 files changed, 18 insertions(+), 8 deletions(-)
--- a/arch/arm64/kernel/pi/map_kernel.c +++ b/arch/arm64/kernel/pi/map_kernel.c @@ -78,6 +78,12 @@ static void __init map_kernel(u64 kaslr_ twopass |= enable_scs; prot = twopass ? data_prot : text_prot;
+ /* + * [_stext, _text) isn't executed after boot and contains some + * non-executable, unpredictable data, so map it non-executable. + */ + map_segment(init_pg_dir, &pgdp, va_offset, _text, _stext, data_prot, + false, root_level); map_segment(init_pg_dir, &pgdp, va_offset, _stext, _etext, prot, !twopass, root_level); map_segment(init_pg_dir, &pgdp, va_offset, __start_rodata, --- a/arch/arm64/kernel/setup.c +++ b/arch/arm64/kernel/setup.c @@ -213,7 +213,7 @@ static void __init request_standard_reso unsigned long i = 0; size_t res_size;
- kernel_code.start = __pa_symbol(_stext); + kernel_code.start = __pa_symbol(_text); kernel_code.end = __pa_symbol(__init_begin - 1); kernel_data.start = __pa_symbol(_sdata); kernel_data.end = __pa_symbol(_end - 1); @@ -281,7 +281,7 @@ u64 cpu_logical_map(unsigned int cpu)
void __init __no_sanitize_address setup_arch(char **cmdline_p) { - setup_initial_init_mm(_stext, _etext, _edata, _end); + setup_initial_init_mm(_text, _etext, _edata, _end);
*cmdline_p = boot_command_line;
--- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -300,7 +300,7 @@ void __init arm64_memblock_init(void) * Register the kernel text, kernel data, initrd, and initial * pagetables with memblock. */ - memblock_reserve(__pa_symbol(_stext), _end - _stext); + memblock_reserve(__pa_symbol(_text), _end - _text); if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && phys_initrd_size) { /* the generic initrd code expects virtual addresses */ initrd_start = __phys_to_virt(phys_initrd_start); --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -561,8 +561,8 @@ void __init mark_linear_text_alias_ro(vo /* * Remove the write permissions from the linear alias of .text/.rodata */ - update_mapping_prot(__pa_symbol(_stext), (unsigned long)lm_alias(_stext), - (unsigned long)__init_begin - (unsigned long)_stext, + update_mapping_prot(__pa_symbol(_text), (unsigned long)lm_alias(_text), + (unsigned long)__init_begin - (unsigned long)_text, PAGE_KERNEL_RO); }
@@ -623,7 +623,7 @@ static inline void arm64_kfence_map_pool static void __init map_mem(pgd_t *pgdp) { static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN); - phys_addr_t kernel_start = __pa_symbol(_stext); + phys_addr_t kernel_start = __pa_symbol(_text); phys_addr_t kernel_end = __pa_symbol(__init_begin); phys_addr_t start, end; phys_addr_t early_kfence_pool; @@ -670,7 +670,7 @@ static void __init map_mem(pgd_t *pgdp) }
/* - * Map the linear alias of the [_stext, __init_begin) interval + * Map the linear alias of the [_text, __init_begin) interval * as non-executable now, and remove the write permission in * mark_linear_text_alias_ro() below (which will be called after * alternative patching has completed). This makes the contents @@ -697,6 +697,10 @@ void mark_rodata_ro(void) WRITE_ONCE(rodata_is_rw, false); update_mapping_prot(__pa_symbol(__start_rodata), (unsigned long)__start_rodata, section_size, PAGE_KERNEL_RO); + /* mark the range between _text and _stext as read only. */ + update_mapping_prot(__pa_symbol(_text), (unsigned long)_text, + (unsigned long)_stext - (unsigned long)_text, + PAGE_KERNEL_RO); }
static void __init declare_vma(struct vm_struct *vma, @@ -767,7 +771,7 @@ static void __init declare_kernel_vmas(v { static struct vm_struct vmlinux_seg[KERNEL_SEGMENT_COUNT];
- declare_vma(&vmlinux_seg[0], _stext, _etext, VM_NO_GUARD); + declare_vma(&vmlinux_seg[0], _text, _etext, VM_NO_GUARD); declare_vma(&vmlinux_seg[1], __start_rodata, __inittext_begin, VM_NO_GUARD); declare_vma(&vmlinux_seg[2], __inittext_begin, __inittext_end, VM_NO_GUARD); declare_vma(&vmlinux_seg[3], __initdata_begin, __initdata_end, VM_NO_GUARD);