From bd024e82e4cd95c7f1a475a55f99871936c2b2db Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 16 Jul 2020 12:28:16 +0100 Subject: asm-generic/mmiowb: Allow mmiowb_set_pending() when preemptible() Although mmiowb() is concerned only with serialising MMIO writes occuring in contexts where a spinlock is held, the call to mmiowb_set_pending() from the MMIO write accessors can occur in preemptible contexts, such as during driver probe() functions where ordering between CPUs is not usually a concern, assuming that the task migration path provides the necessary ordering guarantees. Unfortunately, the default implementation of mmiowb_set_pending() is not preempt-safe, as it makes use of a a per-cpu variable to track its internal state. This has been reported to generate the following splat on riscv: | BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1 | caller is regmap_mmio_write32le+0x1c/0x46 | CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.8.0-rc3-hfu+ #1 | Call Trace: | walk_stackframe+0x0/0x7a | dump_stack+0x6e/0x88 | regmap_mmio_write32le+0x18/0x46 | check_preemption_disabled+0xa4/0xaa | regmap_mmio_write32le+0x18/0x46 | regmap_mmio_write+0x26/0x44 | regmap_write+0x28/0x48 | sifive_gpio_probe+0xc0/0x1da Although it's possible to fix the driver in this case, other splats have been seen from other drivers, including the infamous 8250 UART, and so it's better to address this problem in the mmiowb core itself. Fix mmiowb_set_pending() by using the raw_cpu_ptr() to get at the mmiowb state and then only updating the 'mmiowb_pending' field if we are not preemptible (i.e. we have a non-zero nesting count). Cc: Arnd Bergmann Cc: Paul Walmsley Cc: Guo Ren Cc: Michael Ellerman Reported-by: Palmer Dabbelt Reported-by: Emil Renner Berthing Tested-by: Emil Renner Berthing Reviewed-by: Palmer Dabbelt Acked-by: Palmer Dabbelt Link: https://lore.kernel.org/r/20200716112816.7356-1-will@kernel.org Signed-off-by: Will Deacon --- include/asm-generic/mmiowb.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'include/asm-generic') diff --git a/include/asm-generic/mmiowb.h b/include/asm-generic/mmiowb.h index 9439ff037b2d..5698fca3bf56 100644 --- a/include/asm-generic/mmiowb.h +++ b/include/asm-generic/mmiowb.h @@ -27,7 +27,7 @@ #include DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state); -#define __mmiowb_state() this_cpu_ptr(&__mmiowb_state) +#define __mmiowb_state() raw_cpu_ptr(&__mmiowb_state) #else #define __mmiowb_state() arch_mmiowb_state() #endif /* arch_mmiowb_state */ @@ -35,7 +35,9 @@ DECLARE_PER_CPU(struct mmiowb_state, __mmiowb_state); static inline void mmiowb_set_pending(void) { struct mmiowb_state *ms = __mmiowb_state(); - ms->mmiowb_pending = ms->nesting_count; + + if (likely(ms->nesting_count)) + ms->mmiowb_pending = ms->nesting_count; } static inline void mmiowb_spin_lock(void) -- cgit v1.2.3 From de2b41be8fcccb2f5b6c480d35df590476344201 Mon Sep 17 00:00:00 2001 From: Joerg Roedel Date: Tue, 21 Jul 2020 11:34:48 +0200 Subject: x86, vmlinux.lds: Page-align end of ..page_aligned sections On x86-32 the idt_table with 256 entries needs only 2048 bytes. It is page-aligned, but the end of the .bss..page_aligned section is not guaranteed to be page-aligned. As a result, objects from other .bss sections may end up on the same 4k page as the idt_table, and will accidentially get mapped read-only during boot, causing unexpected page-faults when the kernel writes to them. This could be worked around by making the objects in the page aligned sections page sized, but that's wrong. Explicit sections which store only page aligned objects have an implicit guarantee that the object is alone in the page in which it is placed. That works for all objects except the last one. That's inconsistent. Enforcing page sized objects for these sections would wreckage memory sanitizers, because the object becomes artificially larger than it should be and out of bound access becomes legit. Align the end of the .bss..page_aligned and .data..page_aligned section on page-size so all objects places in these sections are guaranteed to have their own page. [ tglx: Amended changelog ] Signed-off-by: Joerg Roedel Signed-off-by: Thomas Gleixner Reviewed-by: Kees Cook Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20200721093448.10417-1-joro@8bytes.org --- arch/x86/kernel/vmlinux.lds.S | 1 + include/asm-generic/vmlinux.lds.h | 5 ++++- 2 files changed, 5 insertions(+), 1 deletion(-) (limited to 'include/asm-generic') diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 3bfc8dd8a43d..9a03e5b23135 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -358,6 +358,7 @@ SECTIONS .bss : AT(ADDR(.bss) - LOAD_OFFSET) { __bss_start = .; *(.bss..page_aligned) + . = ALIGN(PAGE_SIZE); *(BSS_MAIN) BSS_DECRYPTED . = ALIGN(PAGE_SIZE); diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index db600ef218d7..052e0f05a984 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -341,7 +341,8 @@ #define PAGE_ALIGNED_DATA(page_align) \ . = ALIGN(page_align); \ - *(.data..page_aligned) + *(.data..page_aligned) \ + . = ALIGN(page_align); #define READ_MOSTLY_DATA(align) \ . = ALIGN(align); \ @@ -737,7 +738,9 @@ . = ALIGN(bss_align); \ .bss : AT(ADDR(.bss) - LOAD_OFFSET) { \ BSS_FIRST_SECTIONS \ + . = ALIGN(PAGE_SIZE); \ *(.bss..page_aligned) \ + . = ALIGN(PAGE_SIZE); \ *(.dynbss) \ *(BSS_MAIN) \ *(COMMON) \ -- cgit v1.2.3